Sensor system and methods of making

ABSTRACT

Sensors having an advantageous design and methods for fabricating such sensors are generally provided. Some sensors described herein comprise pairs of electrodes having radial symmetry, pairs of nested electrodes, and/or nanowires. Some embodiments relate to fabricating electrodes by methods in which nanowires are deposited from a fluid contacted with a substrate in a manner such that it evaporates and is replenished.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Application No. 62/953,140, filed Dec. 23, 2019, andentitled “Sensor System and Methods”, to U.S. Provisional ApplicationNo. 62/953,143, filed Dec. 23, 2019, and entitled “Sensor System andElectrodes”, and to U.S. Provisional Application No. 62/953,148, filedDec. 23, 2019, and entitled “Sensor System and Methods of Making”, eachof which is incorporated herein by reference in its entirety.

FIELD

The present invention relates generally to sensors, and, moreparticularly, to sensors suitable for sensing bodily fluids.

BACKGROUND

Sensors may be employed to detect one or more features of bodily fluids.However, some sensors have undesirably low sensitivity to analytes ofinterest. Accordingly, improved sensors are needed.

SUMMARY

Sensors, related components, and related methods are generallydescribed.

Some embodiments relate to sensors. In some embodiments, a sensorcomprises a plurality of pairs of electrodes arranged to have radialsymmetry around a center point. The plurality of pairs of electrodescomprises at least ten pairs of electrodes.

In some embodiments, a sensor comprises a plurality of nanowiresarranged to form a circular structure about a center point and aplurality of electrodes disposed on the plurality of nanowires. Theplurality of nanowires comprises at least 30 nanowires.

In some embodiments, a sensor comprises a pair of electrodes. The pairof electrodes comprises a first electrode comprising a first portion, asecond portion, and a third portion connecting the first and secondportion. The pair of electrodes also comprises a second electrodecomprising a first portion substantially parallel to the first portionof the first electrode, a second portion substantially parallel to thesecond portion of the first electrode, and a third portion connectingthe first and second portions. The first and second portions of thesecond electrode are positioned between the first and second portions ofthe first electrode.

In some embodiments, a sensor comprises a first electrode, a secondelectrode, and a nanowire. The nanowire is in electrical communicationwith the first electrode and the second electrode. A distance betweenthe first electrode and the second electrode is greater than or equal to5 microns and less than or equal to 15 microns. A ratio of a length ofthe nanowire to the distance between the first electrode and the secondelectrode is greater than or equal to 1 and less than or equal to 5.

In some embodiments, a sensor comprises a plurality of pairs ofelectrodes and a plurality of nanowires. For greater than or equal to10% of the pairs of electrodes, the two electrodes making up the pairare in electrical communication by exactly one nanowire.

Some embodiments relate to methods. In some embodiments, a methodcomprises expelling a fluid comprising the plurality of nanowires from anozzle onto the substrate, allowing at least a portion of the fluid toevaporate, replenishing at least a portion of the evaporated fluid byexpelling a further amount of the fluid from the nozzle, and holding thefluid comprising the plurality of nanowires in contact with thesubstrate for a time period of greater than or equal to 0.2 sec. Thefluid is in contact with both the substrate and the nozzle during theholding, replenishing and evaporation steps.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1 shows a pair of electrodes in electrical communication by asingle nanowire, in accordance with some embodiments;

FIG. 2 shows a side view of a pair of electrodes, in accordance withsome embodiments;

FIG. 3 shows a pair of electrodes, in accordance with some embodiments;

FIG. 4 shows a pair of electrodes in electrical communication by asingle nanowire, in accordance with some embodiments;

FIG. 5 shows a side view of a pair of electrodes in a sensor comprisinga blocking layer, in accordance with some embodiments;

FIGS. 6A and 6B show sensors comprising pluralities of pairs ofelectrodes arranged to have radial symmetry around center points, inaccordance with some embodiments;

FIGS. 7A-7E shows sensors comprising pluralities of pairs of electrodesthat are disposed on circular structures comprising pluralities ofnanowires, in accordance with some embodiments;

FIGS. 8A-8E show several steps that may be performed during sensorfabrication, in accordance with some embodiments;

FIGS. 9A-9B show one method of removing a portion of a surface layerfrom a substrate, in accordance with some embodiments;

FIGS. 10A-10E show one method of depositing a pair of electrodes on asubstrate on which a plurality of nanowires is disposed, in accordancewith some embodiments;

FIG. 11 shows one method of forming a passivating layer disposed on anelectrode material, in accordance with some embodiments;

FIG. 12 shows one example of an article comprising a substrate, asurface layer disposed on the substrate, a plurality of nanowiresdisposed on the surface layer, and a pair of passivated electrodesdisposed on the surface layer and the plurality of nanowires, inaccordance with some embodiments;

FIG. 13 shows one non-limiting embodiment of an article comprising alayer positioned between a pair of electrodes and an environmentexternal to the electrodes, in accordance with some embodiments;

FIG. 14 shows one example of an article in which a layer disposed on thepair of electrodes exposes a portion of a plurality of nanowires, aportion of a surface layer, and a portion of each member of the pair ofelectrodes to an environment external thereto, in accordance with someembodiments;

FIG. 15 shows one example of a sensor comprising a wire bondingcomposition disposed on a portion of each member of the pair ofelectrodes, in accordance with some embodiments;

FIG. 16 shows one example of a sensor comprising a blocking layer thatis disposed over a nanowire placing a pair of electrodes in electricalcommunication, but absent from other portions of the sensor, inaccordance with some embodiments;

FIG. 17A shows one non-limiting embodiment of a sensor comprising a pairof electrodes and further comprising a back gate electrode, a water gateelectrode, and a ground electrode, in accordance with some embodiments;

FIG. 17B shows a top view of one exemplary embodiment of a sensorcomprising two further electrodes in addition to a plurality of pairs ofelectrodes, in accordance with some embodiments;

FIG. 17C shows a top view of one exemplary embodiment of a sensorcomprising one further electrode in addition to a plurality of pairs ofelectrodes, in accordance with some embodiments;

FIG. 18 shows one non-limiting example of a sensor comprising anexternal layer, in accordance with some embodiments;

FIG. 19 shows one example of a pair of electrodes comprising oneelectrode including a connecting portion comprising three sub-portions,in accordance with some embodiments;

FIG. 20 is a plot showing current as a function of time, in accordancewith some embodiments; and

FIGS. 21-23 are plots showing equivalent surface potential as a functionof time, in accordance with some embodiments.

DETAILED DESCRIPTION

Sensors, methods of fabricating sensors, and methods of using sensors tosense analytes are generally provided. In some embodiments, a sensordescribed herein has a design that enhances its sensitivity to one ormore analytes of interest.

By way of example, a sensor may comprise a pair of electrodes inelectrical communication via a component having high sensitivity to ananalyte. For instance, a sensor may comprise a pair of electrodes inelectrical communication by a nanowire. The nanowire may have a chemicalcomposition that has a particularly high binding affinity for theanalyte and/or may experience an appreciable change in equivalentsurface potential upon binding with the analyte.

As another example, a sensor may comprise electrodes spaced at anadvantageous distance from each other. The spacing may be selected to belarge enough so that the electrodes may be electrically isolated fromeach other by an insulating material (e.g., large enough such thatphotolithography can be employed to form structures electricallyisolating the electrodes) and small enough such that they can be placedin electrical communication by nanowires that can be commerciallyproduced in sufficiently large quantities. In some embodiments,relatively large spacings between electrodes that are in electricalcommunication by nanowires may be achieved by employing fabricationprocesses that orient the nanowires to form an angle close toperpendicular with the electrodes. For instance, nanowires may bedeposited onto a substrate to form coffee ring structures in which thenanowires are oriented tangentially to one or more circles. Sucharrangements of nanowires may be particularly useful in combination withradially-arranged electrodes, as described in further detail elsewhereherein.

As a third example, a sensor may comprise a blocking layer. The blockinglayer may be positioned between one or more components of the sensor andan environment external to the sensor. In some embodiments, a blockinglayer prevents direct contact between one or more components of thesensor and a fluid to be analyzed by the sensor. The blocking layer maypromote interaction between the sensor and a fluid to be analyzed by thesensor in a desired manner. For instance, it may reduce non-specificinteractions between one or more components of the sensor and one ormore components of the fluid to be analyzed and/or it may reduce chargescreening between a fluid to be analyzed and the sensor. This may beparticularly desirable for sensors designed to sense one or moreanalytes in fluids having a high ionic strength and/or comprisingnumerous components, such as bodily fluids.

As described above, some sensors described herein may have anarrangement of electrodes that facilitates the formation of a sensor inwhich two electrodes are in electrical communication by a nanowire. Insome embodiments, it may be beneficial for the sensor to comprise twoelectrodes that are in electrical communication by exactly one nanowire,as electrodes in electrical communication by exactly one nanowire mayhave a resistivity thereacross that is predictable and/or may be highlysensitive to an analyte of interest. For instance, as described in thepreceding paragraph, a sensor may comprise an arrangement of pairselectrodes in which the pairs of electrodes have radial symmetry arounda center point. Pairs of electrodes having radial symmetry disposed onnanowires arranged to form a circular structure may be particularlylikely to be connected by one such nanowire if the concentration of thenanowires in the circular structure(s) are appropriately selected.

In some embodiments, a sensor comprises electrodes having a design thatfacilitates the formation of a sensor having one or more desirableproperties. By way of example, a sensor may comprise pairs of electrodescomprising an inner electrode nested inside of an outer electrode.Electrodes having this design may be twice as long as parallelelectrodes of the same length, and so may have double the lengthavailable for a nanowire to place in electrical communication.

Some embodiments described herein relate to methods of fabricatingsensors having one or more desirable properties. Such methods maycomprise forming sensors by a process that results in the deposition ofnanowires at a density and/or in an arrangement that is desirable. Forinstance, as described above, some methods may comprise forming one ormore circular structures (e.g., coffee ring structures) of nanowires.The nanowires may be tangentially to the circular structure(s) and/ormay be present in the circular structure(s) at advantageous densities.In some embodiments, a method comprises depositing nanowires from afluid held in contact with a substrate. The fluid may at least partiallyevaporate and/or may be replenished while it is held in contact with thesubstrate. The evaporation and/or replenishment may be selected topromote the formation of coffee ring structure(s) (e.g., having acircular morphology) at desired locations, having desired radii, and/orhaving desired nanowire densities.

FIG. 1 shows one non-limiting embodiment of a pair of electrodes inelectrical communication by a single nanowire. In FIG. 1, a pair ofelectrodes 100 comprises the electrodes 10 and 11. The electrodes 10 and11 are in electrical communication by a nanowire 200. In someembodiments, like the embodiment shown in FIG. 1, a pair of electrodescomprises electrodes that are substantially parallel and/or compriseselectrodes that comprise portions substantially parallel to each other.Electrodes (and/or portions therein) that are relatively parallel toeach other may be oriented such that, if a line were drawn thatintersected with both electrodes (and/or portions) in the pair, theangles that it would make with the two electrodes (and/or portions) inthe pair would differ by a relatively small amount (e.g., less than orequal to 5°, less than or equal to 2°, less than or equal to 1°). Insome embodiments, a pair of electrodes (and/or portions therein) thatare relatively parallel to each other may be oriented such that thedistance between each sub-portion of each electrode (and/or portion ofeach electrode) and the closest sub-portion thereto of the otherelectrode (and/or portion of the other electrode) varies by a relativelysmall amount (e.g., by less than or equal to 2 microns, less than orequal to 1.75 microns, less than or equal to 1.5 microns, less than orequal to 1.25 microns, less than or equal to 1 micron, less than orequal to 0.75 microns, or less than or equal to 0.5 microns).Additionally, it should also be understood that pairs of electrodeslacking substantially parallel portions are also contemplated.

A nanowire may place a pair of electrodes in electrical communicationwhen it itself is in electrical communication with both members of thepair and when it provides a pathway through which current can flowbetween the pair of electrodes. This may be determined by applying a 0.1V potential across the pair of electrodes and measuring the resultantcurrent therebetween. If the resultant current is greater than or equalto 1 nA, then the pair of electrodes may be considered to be inelectrical communication with each other.

In some embodiments, a nanowire that places two electrodes in electricalcommunication may be oriented such that it is at an angle to one or bothelectrodes that is close to 90°. With reference to FIG. 1, an angle (theangle 0) between a nanowire (the nanowire 200 in FIG. 1) and a directionperpendicular to an electrode (the direction 300 in FIG. 1 perpendicularto the electrode 10 in FIG. 1) may be relatively low. As describedelsewhere herein, a nanowire having this property may be able to placeelectrodes in electrical communication that are spaced at a distanceclose to the length of the nanowire. This may advantageously allow forelectrodes to be spaced apart at distances that allow them to beseparated by photolithographic structures and/or may allow for the useof nanowires that have a length capable of being fabricated bycommercial processes in an economical and/or relatively defect-freemanner. However, it should also be understood that some nanowires may beoriented at a variety of angles to two electrodes that it places inelectrical communication.

FIG. 2 shows a side view of the pair of electrodes shown in FIG. 1. Likein FIG. 2, some embodiments comprise a pair of electrodes disposed on ananowire. It is also possible for a nanowire to be disposed on a pair ofelectrodes (e.g., alternatively to the pair of electrodes being disposedon the nanowire). Components disposed on each other as described hereinand/or shown in the figures herein may be directly disposed on eachother or may be indirectly disposed on each other. In other words, asused herein, when a component is referred to as being “disposed on” or“adjacent” another component, it can be directly disposed on or adjacentthe component, or it may be disposed on one or more interveningcomponents disposed on the other component. A component that is“directly disposed on”, “directly adjacent” or “in contact with” anothercomponent means that it is disposed on the other component in a mannersuch that no intervening component is present.

FIG. 3 shows another possible electrode design. In FIG. 3, a pair ofelectrodes 102 comprises an electrode 12 (e.g., a first electrode) andan electrode 22 (e.g., a second electrode). Like the electrodes shown inFIGS. 1-2, electrodes having this design may also be in electricalcommunication by a nanowire (e.g., as shown in FIG. 4, in which theseelectrodes are electrically connected by a nanowire 202). The electrodesshown in FIGS. 3 and 4 each have three portions: a first and secondportion that are substantially parallel to each other (the portions 22Aand 22B of the electrode 22 and the portions 12A and 12B of theelectrode 12 as shown in FIG. 3) and one portion connecting the firstand second portions (the portion 22C of the electrode 22 and the portion12C of the electrode 12 as shown in FIG. 3). As shown in FIGS. 3 and 4,the electrodes may be nested such that the first and second portions ofthe second electrode are positioned between the first and secondportions of the first electrode (e.g., such that the portions 12A and12B of the electrode 12 shown in FIG. 3 are positioned between theportions 22A and 22B of the electrode 22 shown in FIG. 3). Similarly, asis shown in FIGS. 3 and 4, the electrodes may be arranged such thatportions of each electrode are parallel to portions of the otherelectrode. By way of example, with reference to FIG. 3, the portion 12Aof the electrode 12 is parallel to the portion 22A of the electrode 22and the portion 12B of the electrode 12 is parallel to the portion 22Bof the electrode 22.

The electrodes described herein may be positioned in the sensorsdescribed herein. The sensors may further comprise one or moreadditional components. One example of such a component is a blockinglayer. As described above, a blocking layer may be disposed on one ormore portions of the sensor and/or may be configured to prevent directcontact between one or more portions of the sensor and environmentexternal to the sensor. FIG. 5 shows one example of a side view of apair of electrodes in a sensor comprising a blocking layer. In FIG. 5,the pair of electrodes 14 and 24 are in electrical communication by ananowire 204. A blocking layer 404 is disposed over the nanowire 204. Insome embodiments, the blocking layer may be the only layer positionedbetween a nanowire and an environment external to the sensor.Accordingly, it may mediate interactions between the environmentexternal the sensor and the nanowire (e.g., between a fluid disposed onthe sensor and the nanowire).

It should be understood that FIG. 5 is merely exemplary and that someblocking layers may differ from those shown in FIG. 5. For instance,some blocking layers may have different thicknesses with respect to thenanowire and/or the electrodes than the blocking layer shown in FIG. 5.As another example, some blocking layers may extend such that they arealso at least partially disposed on one or both electrodes in a pair ofelectrodes. Similarly, it should be understood that some sensors maycomprise further components than those shown in FIG. 5, non-limitingexamples of which include substrates, surface layers, wire bonding pads,and/or further electrodes.

In some embodiments, a sensor comprises a plurality of pairs ofelectrodes. Some of the pairs of electrodes may be in electricalcommunication (e.g., by a single nanowire, by more than one nanowire)and/or some of the pairs of electrodes may not be in electricalcommunication with one another. As described elsewhere herein, in someembodiments, a sensor comprises a plurality of pairs of electrodesarranged in a manner that promotes the formation of electricalcommunication between pairs of electrodes by a single nanowire. Forinstance, in some embodiments, a sensor comprises a plurality of pairsof electrodes arranged to have radial symmetry around a center point.FIG. 6A shows one non-limiting embodiment of a sensor having thisproperty. In FIG. 6A, a sensor 1006 comprises pairs of electrodes106A-106J arranged radially symmetrically around a center point 506.Some sensors may have one or more features like the sensor shown in FIG.6A (e.g., some sensors may comprise exactly ten pairs of electrodes),and some sensors may differ from the sensor shown in FIG. 6A in one ormore ways (e.g., some sensors may comprise a different number of pairsof electrodes, may comprise electrodes having a different design thanthe electrodes shown in FIG. 6A and/or may be spaced from the centerpoint at distances other than those shown in FIG. 6A).

It should also be understood that the center point may lack anydistinguishing feature (e.g., it may be the geometric center aroundwhich the electrodes are positioned in a radially symmetric manner, butotherwise have a chemistry and/or structure consistent with portions ofthe sensor to which it is adjacent) or may comprise one or morestructural and/or chemical features distinguishing it from otherportions of the sensor (e.g., it may comprise an electrode or otherfunctional portion of the sensor).

FIG. 6B shows another example of a sensor comprising a plurality ofpairs of electrodes arranged to have radial symmetry around a centerpoint. In FIG. 6B, a motif 106K comprising 13 pairs of electrodes isarranged to have radial symmetry around the center point 506. Inembodiments in which a motif is arranged to have radial symmetry arounda center point, the motif may comprise a variety of suitable numbers ofpairs of electrodes. For instance, the motif may comprise two or more,three or more, four or more, five or more, six or more, seven or more,eight or more, nine or more, ten or more, eleven or more, twelve ormore, thirteen or more, fourteen or more, fifteen or more, sixteen ormore, seventeen or more, eighteen or more, nineteen or more, or twentyor more pairs of electrodes.

A plurality of pairs electrodes that have radial symmetry around a pointmay be positioned with respect to the point such that rotation of thepair of electrodes by a given angle (e.g., by 36° for ten electrodesthat have radial symmetry) results in a plurality of pairs of electrodeshaving a structure substantially identical to the structure of theplurality of pairs of electrodes prior to rotation. In some embodiments,a plurality of pairs electrodes that have radial symmetry around a pointcomprises a structural motif (e.g., a pair of electrodes, a pair ofelectrodes exclusive of any leads connecting the pair of electrodes toanother component of the sensor and/or an environment external to thesensor) that is positioned with respect to the point such that rotationof the pair of electrodes by a given angle (e.g., by 36° for tenelectrodes that have radial symmetry) results in the structural motifbeing arranged substantially identically to the way that it was arrangedprior to rotation. In some embodiments, a plurality of pairs ofelectrodes having radial symmetry may be positioned such that they(and/or a structural motif therein) are separated from each other byequal angles. By way of example, a plurality of electrodes may compriseten pairs of electrodes, each of which are oriented with respect totheir nearest neighbors such that rotation of any given pair ofelectrodes by 36° clockwise or counterclockwise around the center pointwould cause the pair of electrodes (and/or a structural motif therein)to substantially overlap with their clockwise or counterclockwisenearest neighbor, respectively. As another example, a plurality ofelectrodes may comprise twenty pairs of electrodes, each of which areoriented with respect to their nearest neighbors such that rotation ofany given pair of electrodes by 18° clockwise or counterclockwise aroundthe center point would cause the pair of electrodes (and/or a structuralmotif therein) to substantially overlap with their clockwise orcounterclockwise nearest neighbor, respectively.

As can be seen from FIGS. 6A and 6B, some pluralities of pairs ofelectrodes that are arranged to have radial symmetry around a centerpoint are made up of pairs electrodes that oriented with respect to thecenter point in a manner such that each pair of electrodes can be mappedonto each other pair of electrodes by rotation around the center pointand some pluralities of pairs of electrodes comprise at least some pairsof electrodes that cannot be mapped onto other pairs of electrodes bysuch rotation. In some embodiments, a plurality of pairs of electrodesforms a plurality of structural motifs that have radial symmetry arounda center point such that each structural motif can be mapped onto eachother structural motif by rotation around the center point.

In some embodiments, a plurality of pairs of electrodes have a type ofsymmetry other than radial (e.g., in addition to radial symmetry,instead of radial symmetry). For instance, in some embodiments, aplurality of pairs of electrodes has reflection symmetry. In such cases,the plurality of pairs of electrodes may be positioned with respect toone or more mirror planes such that reflection of the pair of electrodesacross the mirror plane(s) results in a plurality of pairs of electrodeshaving a structure substantially identical to the structure of theplurality of pairs of electrodes prior to reflection. Similarly, theplurality of pairs of electrodes may comprise a structural motif (e.g.,a pair of electrodes, a pair of electrodes exclusive of any leadsconnecting the pair of electrodes to another component of the sensorand/or an environment external to the sensor) that is positioned withrespect to one or more mirror planes such that reflection of the pair ofelectrodes across the mirror plane(s) does not change the arrangement ofthe structural motifs.

Additionally, some sensors may comprise a plurality of pairs ofelectrodes that is equidistant from a center point but not necessarilyradially symmetric about the center point. As an example, a sensor maycomprise a plurality of pairs of electrodes that is positioned to beequidistant from the center point but not positioned equiangularlyaround the center point. For instance, a sensor may comprise fourelectrodes and each electrode may comprise one nearest neighbor fromwhich it is separated by a rotation of less than 90° (e.g., less than orequal to 85°, less than or equal to 80°, less than or equal to 85°, lessthan or equal to 70°, less than or equal to 75°, less than or equal to60°) and/or one nearest neighbor from which it is separated by arotation of greater than 90° (e.g., greater than or equal to 95°,greater than or equal to 95°, greater than or equal to 100°, greaterthan or equal to 105°, greater than or equal to 110°, greater than orequal to 115°, or greater than or equal to 120°). As another example, asensor may comprise a plurality of structural motifs comprising one ormore pairs of electrodes (e.g., as shown in FIG. 6B) that are positionedequidistantly from a center point but not radially symmetrically aboutthe center point. For instance, a sensor may comprise four suchstructural motifs and each structural motif may comprise one nearestneighbor from which it is separated by a rotation of less than 90°and/or one nearest neighbor from which it is separated by a rotation ofgreater than 90°. For instance, with respect to FIG. 7E, the angle 6 maybe a value other than 90° (e.g., less than 90° or greater than 90°).

In some embodiments, a sensor comprises a plurality of electrodes thatare equidistant from a center point but lack an angle of less than 360°through any given pair of electrodes can be rotated to overlap withanother plurality of electrodes. This may be due to differingorientations of the electrodes, different shapes of the electrodesand/or different sizes of the electrodes. Similarly, a sensor maycomprise a plurality of structural motifs comprising one or more pairsof electrodes that are equidistant from a center point but lack an angleof less than 360° through any given motif can be rotated to overlap withanother structural motif. This may be due to differing orientations ofthe structural motifs and/or electrodes therein, different shapes of thestructural motifs and/or electrodes therein and/or different sizes ofthe structural motifs and/or electrodes therein.

Additionally, a sensor may comprise a plurality of pairs of electrodesand/or a plurality of structural motifs that are not equidistant from acenter point that are positioned within a range of distances from thecenter point. For instance, as described in further detail below, theplurality of pairs of electrodes and/or plurality of structural motifsmay be positioned within a range of distances from the center pointsthat overlaps (e.g., partially, fully) with a circular structurecomprising a plurality of nanowires.

As shown in FIGS. 7A and 7B, it is also possible for a sensor tocomprise a plurality of pairs of electrodes that are disposed on acircular structure comprising and/or formed from a plurality ofnanowires (e.g., on the circular structure 606 shown in FIGS. 7A and7B). As shown in FIGS. 7A and 7B, such electrodes may have radialsymmetry around a center point. The circular structure may also haveradial symmetry around this same center point and/or may comprise pairsof electrodes positioned equidistantly from this same center point. Insome embodiments, at least a portion of the nanowires forming thecircular structure may be oriented substantially tangentially to thecircular structure. As described elsewhere herein, such nanowires mayintersect one or more electrodes at an angle close to 90° and/or may bein electrical communication with two electrodes in a pair of electrodeswhile also having a length relatively close to the distancetherebetween. It is also possible for the nanowires in a circularstructure to be oriented randomly therein and/or for one or moreportions of the nanowires in the circular structure to be orientedrandomly (e.g., in addition to one or more portions orientedsubstantially tangentially to the circular structure). It should beunderstood that references to “circular structures” herein may refer tostructures that form a perfect geometric circle or may refer tostructures that form a shape close to a perfect geometric circle butthat differ insubstantially from a perfect geometric circle in one ormore ways. Although the circular structures shown in FIGS. 7A and 7Bhave relatively small widths in comparison to the pluralities of pairsof electrodes also shown therein, it is also possible for circularstructures to have widths that are on the order of the sizes of thesepluralities of pairs of electrodes and/or motifs formed by thesepluralities of pairs of electrodes. For instance, FIGS. 7C and 7D showcircular structures having widths that are large enough to cover thepluralities of electrodes shown therein. These widths are labeled W inboth of these figures.

In some embodiments, a sensor described herein may be configured tosense a single analyte. In such embodiments, all of the nanowires may befunctionalized to have a single type of chemistry (e.g., a single typeof functional group, a single type of binding entity). Other sensors maybe configured to sense two or more analytes. Such sensors may comprisetwo or more groups of nanowires that are functionalized with differentchemistries (e.g., different types of functional groups, different typesof binding entities). In some embodiments, a plurality of pairs ofelectrodes may be arranged such that there are groups of electrodes thatcorrespond to groups of nanowires that are functionalized with differentchemistries. Such groups of electrodes may comprise a number and/orarrangement of electrodes that results in a relatively high number ofelectrodes in electrical communication with each other by the nanowiresin the relevant group and/or that results in a relatively small (orzero) number of electrodes in electrical communication with each otherby nanowires outside the relevant group. Such groups of electrodes mayhave shapes that roughly correspond to the areas over which the speciesemployed to functionalize the nanowires can be facilely dispensed. Forinstance, FIG. 7E shows four examples of areas over which the speciesemployed to functionalize the nanowires can be facilely dispensed (theareas 696A, 696B, 696C, and 696D). As can be seen from FIG. 7E, a groupof electrodes is positioned within each area. These areas may also haveradial symmetry about a center point, be positioned equidistantly from acenter point, and/or be positioned within a range of distances from acenter point (e.g., the same center point about which a plurality ofpairs of electrodes and/or structural motifs has radial symmetry, thesame center point about which a circular structure of nanowires hasradial symmetry)

It should be understood that sensors having designs similar to thoseshown in FIGS. 6 and 7 may comprise electrodes having a variety ofsuitable designs. In some embodiments, the pairs of electrodes have adesign similar to that shown in FIG. 3. It is also possible for thepairs of electrodes to have a design similar to that shown in FIG. 1(e.g., the sensor may comprise an array of linear electrodes positionedsuch that their long axes are next to each other).

As described elsewhere herein, some embodiments relate to methods offabricating sensors and/or methods that may be performed during thefabrication of sensors (e.g., sensors having one or more of the featuresdescribed herein). FIGS. 8A-8D show one method that may be performedduring sensor fabrication (e.g., in combination with other, furthersteps). The method shown in FIGS. 8A-8D depicts one manner in which aplurality of nanowires may be deposited onto a substrate. The methodcomprises expelling a fluid comprising the plurality of nanowires from anozzle and holding the fluid comprising the plurality of nanowires incontact with both the substrate and the nozzle for a finite period oftime. During this finite period of time, at least a portion of the fluidis allowed to evaporate and is replenished by further fluid from thenozzle. FIGS. 8A-8B shows the expulsion of a fluid 708 comprising aplurality of nanowires from a nozzle 808 onto a substrate 908. FIG. 8Cshows the fluid 708 comprising the nanowires after partial evaporation,and FIG. 8D shows the fluid 708 comprising the nanowires afterreplenishment. FIG. 8E shows a top view of FIG. 8D. Although FIGS. 8Cand 8D show fluid evaporation and replenishment as distinct steps, itshould be understood that both may occur simultaneously. For instance,fluid from the fluid comprising nanowires may be continually evaporatingthroughout the process shown in FIGS. 8A-8D. As another example, thefluid may be continually replenished throughout the process shown inFIGS. 8A-8D and/or may be replenished at discrete times (e.g.,periodically) during which evaporation also occurs.

The method shown in FIGS. 8A-8D may be advantageous for forming circularstructures comprising nanowires at advantageous locations and/ororiented at advantageous angles. Without wishing to be bound by anyparticular theory, it is believed that this method may be suitable forforming such structures due to the coffee ring effect. The coffee ringeffect may occur when fluid comprising a solid (in some embodimentsdescribed herein, a plurality of nanowires) at least partiallyevaporates at its surface (e.g., at an interface between the fluid andair). As the fluid evaporates from its surface, the solid suspendedand/or dissolved therein does not evaporate and so may becomeincreasingly concentrated at the surface of the fluid. Additionally,evaporation of a fluid from its surface may cause further transport offluid from its interior to its surface, transporting further solids fromthe interior of the fluid to its surface. This is believed to result inthe formation of a relatively large concentration of the solid at theexternal boundary of the fluid at which evaporation occurs (e.g., aninterface between the fluid and air; an interface between the fluid,air, and a substrate on which the fluid is disposed; an outer rim of thefluid). If the fluid is pinned at a particular location on a substrateduring such evaporation (e.g., due to surface tension), a coffee ring orcircular structure comprising the solids therein (e.g., nanowires)disposed on that location may form after evaporation of the fluid.

The methods described herein, such as the method shown in FIGS. 8A-8Dmay be suitable for forming coffee ring structures or circularstructures at desired locations because they may allow for placement ofthe surface of the fluid from which evaporation may occur (and, in someembodiments, the associated placement of solids therein on a substrateon which the fluid is disposed during evaporation). For instance, theinitial volume of the fluid comprising the plurality of nanowires may beselected such that the outer boundary of the fluid on the substrate isat a location where it is desirable for a coffee ring and/or circularstructure to form. As another example, the initial concentration of thenanowires in the fluid, the rate at which the fluid is replenished,and/or the total amount of fluid evaporated may be selected such thatthe coffee ring and/or circular structure that forms has a desirabledensity of nanowires. In some embodiments, the rate at which the fluidevaporates may be adjusted (e.g., by selection of the fluid, bytemperature of the substrate) to promote formation of a coffee ring orcircular structure having one or more desirable properties. Combinationsof the above-mentioned parameters may be varied to tailor the depositionof the plurality of nanowires.

As described herein, in some embodiments a method may involve forming acircular structure comprising a plurality of nanowires. The method mayalso involve forming a plurality of pairs of electrodes (e.g., at leastten pairs of electrodes) arranged to have radial symmetry around acenter point such that at least one nanowire is in electricalcommunication with one pair of electrodes. As a result, in someembodiments, a sensor comprises a plurality of nanowires arranged toform a circular structure (e.g., a circular structure having radialsymmetry around a center point) and a plurality of electrodes disposedthereon (e.g., a plurality of electrodes also having radial symmetryaround the same center point). In some embodiments, for greater than orequal to 10% of the pairs of electrodes, the two electrodes making upthe pair are in electrical communication by exactly one nanowire.

In some embodiments, a plurality of nanowires is deposited onto asubstrate that has been plasma etched (e.g., as described elsewhereherein). The plasma etching may advantageously enhance the uniformity ofthe surface thereof. In the case of a silicon substrate, the plasmaetching may cause the formation of hydroxyl groups that enhance bondingbetween the plurality of nanowires and the substrate surface.

As described above, some embodiments relate to sensors comprisingcomponents other than those shown in FIGS. 1-7 (e.g., in addition to thecomponents shown in one or more of FIGS. 1-7) and/or relate to methodsof fabricating sensors comprising steps other than those shown in FIGS.8A-8D (e.g., in addition to the steps shown in FIGS. 8A-8D). An overviewof one set of steps by which a sensor can be fabricated is providedbelow. The components that the sensor may comprise are introduced belowin combination with a step by which they may be fabricated. However, itshould be understood that some sensors may comprise such component(s)but that the component(s) may be fabricated in a manner other than thatdescribed. It should also be understood that some sensors may compriseall of the components below, some sensors may comprise a subset of thecomponents below, and/or some sensors may comprise components other thanthose described below. Similarly, it should be understood that somemethods may comprise all of the steps below, some methods may comprise asubset of the steps below, and/or some methods may comprise steps otherthan those described below.

In some embodiments, a sensor is disposed on a substrate. Somesubstrates naturally and/or by design comprise a layer disposed thereonhaving a different chemical composition than the substrate bulk. It maybe desirable to remove at least a portion of this surface layer from thesubstrate so that one or more components of the sensor may be fabricateddirectly on the substrate and/or so that portion(s) of the substrateuncovered by a surface layer may serve as fiducial alignment marks.Direct fabrication of one or more components of the sensor on thesubstrate may be employed when it is desirable for the relevantcomponent(s) to be in direct electrical communication with thesubstrate, such as when the substrate is employed as a gating electrodeand/or when the substrate is grounded. Fiducial alignment marks may beemployed during further sensor fabrication steps to ensure that theprocesses performed are performed at the correct location(s) on thesubstrate. For instance, the location(s) at which further sensorfabrication steps are be performed may be determined with reference toone or more fiducial alignment marks. If multiple steps are performed atlocation(s) at known distances from the fiducial alignment mark(s), theymay thus be performed at known distances from each other.

FIGS. 9A-9B show one method of removing a portion of a surface layerfrom a substrate. In FIGS. 9A-9B, a portion of a surface layer 2010 isremoved from a substrate 910 to form an article comprising a substrateon which a surface layer is partially disposed. In some embodiments,such a process may be performed to form an article in which one or moreportions of the substrate is/are covered by a surface layer and one ormore portions of the substrate is/are uncovered by a surface layer(e.g., they may be directly exposed to an environment external to thesubstrate). Such a process may also be formed to remove the entirety ofa surface layer from a substrate (not shown).

A surface layer may be removed from a substrate by a variety of suitabletechniques. In some embodiments, an etching technique may be used,non-limiting examples of which include wet etching techniques and dryetching techniques. Wet etching techniques may comprise exposing thesubstrate to a wet etchant. One example of a suitable wet etchant is asolution comprising an acid (e.g., hydrofluoric acid) and a bufferingagent (e.g., ammonium fluoride). The acid and the buffering agent may bemixed at a variety of ratios, such as a 1:6 buffering agent:acid ratio.Another example of a suitable wet etchant is an acid (e.g., hydrofluoricacid). Dry etching techniques may comprise exposing the substrate to adry etchant, such as a reactive plasma (e.g., a reactive oxygen plasma).The plasma may be generated by exposing a low pressure environment to anelectromagnetic field to generate high energy ions. The high energy ionsmay attack the passivating layer and etch it away. In one exemplaryembodiment, a plasma etch is performed by exposing the substrate to anoxygen plasma at a pressure of 1 Torr and a power of 50 W in a Plasmalin115 plasma etcher.

The time for which an etching technique may be performed may be selectedsuch that the surface layer is removed but that the underlying substrateis not appreciably etched. For this reason, it may vary with thethickness of the surface layer. For the case of a solution comprising anacid and a buffering agent, which may remove a surface layer at a rateof approximately 100 nm/minute, a suitable exposure time of thesubstrate to the solution in minutes may be determined by dividing thethickness of the surface layer in nanometers by 100.

When an etching process is performed to remove a portion, but not all,of a surface layer, the portions of the surface layer designed to beretained may be protected from exposure to the etchant during theetching process. In some embodiments, the portion(s) of the surfacelayer designed to be retained may be covered by a photoresist during theetching process while the portion(s) of the surface layer designed to beremoved may be free from the photoresist. After the etching process, theremainder of the photoresist may be removed. Suitable photoresists (andassociated methods of patterning photoresists) include those describedelsewhere herein as options for forming photoresist layers to beincluded in the final sensor (e.g., photoresists that may be patternedby selective exposure to light and then subsequent development, such asAZ-5214E-IR, SU8).

It should also be noted that some sensors may comprise fiducialalignment marks other than those formed by etching away portions of apassivating layer disposed on a substrate. By way of example, somesensors may comprise fiducial alignment marks formed by depositing amaterial on a substrate. Non-limiting examples of suitable suchmaterials include metals (e.g., nickel, chromium, gold, titanium,platinum, aluminum, alloys thereof, combinations thereof).

As described above, some embodiments may comprise a plurality ofnanowires disposed on a substrate. The plurality of nanowires may bedeposited on the substrate after at least a portion of a surface layerdisposed on the substrate has been removed therefrom and/or afterfiducial alignment marks have been formed thereon. In some embodiments,the plurality of nanowires are deposited onto a surface layer disposedon a substrate.

As also described above, some embodiments may comprise pairs ofelectrodes disposed on a substrate. The pairs of electrodes may bedisposed on the substrate (e.g., directly on a surface layer disposedthereon) and/or may be disposed on a portion of the plurality ofnanowires (e.g., directly thereon). A variety of suitable techniques maybe employed to deposit a pair of electrodes on a substrate. In someembodiments, a pair of electrodes is deposited on a substrate by vapordeposition. Prior to vapor deposition of the electrodes, a photoresistmay be deposited onto the substrate and selectively removed fromlocations at which the electrodes are to be deposited. By way ofexample, a photoresist may be deposited onto the substrate, exposed tolight (e.g., UV light) through a mask at the locations at which thepairs of electrodes are to be deposited, and then exposed to adeveloper. The developer may remove the portions of the photoresistexposed to the light. Then, the material forming the pairs of electrodesmay be deposited onto both the photoresist and the exposed nanowiresand/or substrate therebeneath. This material forming the pairs ofelectrodes may thus deposit directly onto the nanowires and/or substratein the locations where the photoresist has been removed.

FIGS. 10A-10E show one method of depositing a pair of electrodes on asubstrate on which a plurality of nanowires is disposed. FIG. 10A showsa substrate 912 on which a surface layer 2012 is disposed. The plurality212 of nanowires is disposed thereon. In FIG. 10B, a photoresist 3012has been deposited on the plurality of nanowires 212. FIG. 10C shows theexposure to light of portions 3112 and 3212 of the photoresist, and FIG.10D shows the substrate, nanowires, and photoresist after removal ofportions 3112 and 3212 of the photoresist upon exposure to a developer.FIG. 10E depicts the deposition of an electrode material on thephotoresist, plurality of nanowires, and substrate to form a pair ofelectrodes 112. It is noted that nanowire 213 in the plurality ofnanowires 212 is in direct contact and electrical communication withboth electrodes in the pair of electrodes 112. It is also noted that thepair of electrodes 112 is in electrical communication with each other bythe nanowire 213.

In some embodiments, a process may be formed after the step shown inFIG. 10D and the step shown in FIG. 10E. By way of example, thesubstrate and/or nanowires disposed thereon may be prepared fordeposition of the electrode material. For instance, any portions of thenanowire unsuitable for forming an ohmic contact with the electrodematerial may be removed (e.g., any oxide thereon). This may beaccomplished by etching the surfaces of the nanowires, such as byexposing the nanowires to an etchant (e.g., by dipping the substrate inan etchant, by performing a plasma etch). The etchant may be the sametype of etchant suitable for removing a surface layer from a substratedescribed above and/or the etching process may be the same etchingprocess described above with respect to forming fiducial alignment marksin a surface layer. The etching time may be selected to be sufficient toremove the desired material from the nanowires (e.g., any oxide on thenanowires) but not sufficient to remove desirable components of thesubstrate (e.g., all of the oxide on the substrate). For instance, insome embodiments, the etching time may be selected to be sufficient toremove approximately several nanometers of oxide but insufficient toremove hundreds of nanometers of oxide (e.g., sufficient to remove 2-5nm of oxide but insufficient to remove 300-600 nm of oxide). As anotherexample of a process that may be performed after the steps shown inFIGS. 10D and 10E, the substrate and/or nanowires disposed thereon maybe cleaned by exposure to a solvent and then spun dry. The solvent maycomprise an organic solvent and/or may comprise water (e.g., deionizedwater). Non-limiting examples of suitable organic solvents includeacetone and alcohols (e.g., methanol, isopropanol).

After formation of the pairs of electrodes, the surfaces of the pair(s)of electrodes may be passivated. For instance, a passivating layer maybe formed thereon. The surfaces may be passivated by exposure to a gasthat reacts with the electrodes to alter their surface chemistry and/ormay be passivated by depositing a material thereon (e.g., from a gas,from a liquid). If the pairs of electrodes are formed with theassistance of a photoresist as shown in FIGS. 10A-10E, the entiresurface of the electrode material may be passivated (e.g., the surfaceof the electrode material forming the pair(s) of electrodes and thesurface of the electrode material disposed on the photoresist). It isalso possible for only the electrode surfaces to be passivated (e.g., inthe case where pair(s) of electrodes are fabricated by another method,in the case where electrode material not forming the pair(s) ofelectrodes is removed prior to the passivation process). FIG. 11 showsone method of forming a passivating layer 4014 disposed on the electrodematerial. Passivating the surfaces of the pair(s) of electrodes mayadvantageously reduce the reactivity of the material forming theelectrodes and/or protect the material forming the electrodes duringfurther fabrication steps.

As described above, methods comprising forming electrodes with theassistance of a photoresist may comprise removing the photoresist andany electrode material disposed thereon from the substrate. This stepmay allow for the deposition of further, non-electrode material onto oneor more portions of the substrate covered by the photoresist duringelectrode formation. The photoresist may be removed directly afterdeposition of the electrode material (e.g., prior to passivation of thesurface of the electrode material or any other further steps), directlyafter passivation of the surface of the electrode material (e.g., andprior to any other further steps), or at a later point in time (e.g.,after the formation of ohmic contacts between the electrodes and thenanowires to which they are directly adjacent). The photoresist may beremoved from the substrate by, for example, exposing it to a solvent inwhich it is soluble. FIG. 12 shows one example of an article comprisinga substrate 916, a surface layer 2016 disposed on the substrate, aplurality of nanowires 216 disposed on the surface layer, and a pair ofpassivated electrodes 116 disposed on the surface layer and theplurality of nanowires.

Another step that may be performed subsequent to the deposition ofpair(s) of electrodes is the formation of ohmic contacts between theelectrodes and the nanowire(s) to which the electrodes are directlyadjacent. This step may be performed after passivating the surfaces ofthe pair(s) of electrodes, prior to passivating the surfaces of thepair(s) of electrodes, or as a step in a method that does not comprisepassivating the surfaces of the pair(s) of electrodes. In someembodiments, it may be advantageous to passivate the surfaces of thepair(s) of electrodes prior to formation of the ohmic contacts becausethe method employed to form the ohmic contacts may be performed in amanner such that the electrodes are exposed to an environment that wouldpromote one or more deleterious reactions at the electrode surfaces ifunpassivated but for which passivated electrode surfaces may berelatively unreactive. By way of example, in some embodiments, the ohmiccontacts may be formed by exposing the electrodes and the plurality ofnanowires to a heated environment and/or an environment comprising oneor more gases reactive with the electrode surfaces. It may also beadvantageous to remove any photoresist disposed on the substrate priorto formation of the ohmic contacts for similar reasons. Manyphotoresists that may be desirable for use in forming electrodes may beundesirably reactive under the conditions present during ohmic contactformation.

A fourth step that may be performed subsequent to the deposition ofpair(s) of electrodes is the formation of a layer positioned between thepair(s) of electrodes and an environment external to the electrodes. Alayer having this property may electrically insulate the electrodes fromthe environment external thereto, which may advantageously prevent theformation of short circuits when the electrodes are exposed to anenvironment that is electrically conductive (e.g., an aqueousenvironment). This step is typically performed subsequent to the step ofpassivating the surfaces of the electrodes. It may be performedsubsequent to the step of removing any photoresist deposited on thesubstrate and/or the step of forming an ohmic contact between theelectrodes and the nanowires to which they are directly adjacent. Thelayer positioned between the pair(s) of electrodes and an environmentexternal to the electrodes may be formed by a variety of suitableprocesses, including vapor deposition and/or spin coating.

FIG. 13 shows one non-limiting embodiment of an article comprising alayer positioned between a pair of electrodes and an environmentexternal to the electrodes. In FIG. 13, the layer 5018 is disposed onthe pair of electrodes 118, the plurality of nanowires 218, and thesurface layer 2018 that are all disposed on the substrate 918. Thislayer isolates these components of the article from an environmentexternal thereto. Example 1 provides a description of one exemplarymethod by which an electrically insulating layer positioned at thislocation may be formed.

Some layers positioned between a pair of electrodes and an environmentexternal thereto may be disposed over the entirety of an externalsurface of the article comprising the pair of electrodes (e.g., as shownin FIG. 13). In other embodiments, an article may comprise a layerpositioned between a pair of electrodes and an environment external tothe electrodes that exposes one or more portions of the article to theenvironment external to the electrodes. By way of an example, in someembodiments, a layer positioned between a pair of electrodes and anenvironment external to the electrodes does not cover a portion of thenanowires in the plurality of nanowires (e.g., one or more nanowires inelectrical communication with one or both of the electrodes in the pairof electrodes), one or more portions of the surface layer disposed onthe substrate, one or more portions of the substrate (e.g., one or moreportions of the substrate from which a surface layer disposed thereonhas been etched away to form a fiducial alignment mark), and/or one ormore portions of the electrodes configured to be isolated from anenvironment external thereto by a different component. FIG. 14 shows oneexample of an article in which the layer 5020 disposed on the pair ofelectrodes 120 exposes a portion of the plurality of nanowires 220, aportion of a surface layer 2020, and a portion of each member of thepair of electrodes 120 to an environment external thereto. A layerpositioned between a pair of electrodes and an environment external tothe electrodes that exposes one or more other components of the articlein which it is positioned may be fabricated to do so by use of aphotoresist that can be patterned through a mask as described elsewhereherein.

In some embodiments, a method of fabricating a sensor comprises forminga component that places one or more pairs of electrodes therein in inelectrical communication with an environment external to the sensor.This step is typically performed after formation of the pair(s) ofelectrodes and after formation of a layer positioned between the pair(s)of electrodes and an environment external to the electrodes. In suchcases, one or more portions of the layer positioned between the pair(s)of electrodes and an environment external to the electrodes may beremoved therefrom (e.g., as described in the preceding paragraph), and acomposition configured to place the electrodes and an environmentexternal thereto may be deposited on the electrode at the location(s)from which this layer was removed. It is also possible for a componentthat places one or more pairs of electrodes therein in electricalcommunication with an environment external to the sensor to be formedprior to the formation of a layer positioned between the pair(s) ofelectrodes and an environment external to the electrodes and/or to beformed in embodiments which lack a layer positioned between the pair(s)of electrodes and an environment external to the electrodes.

Similarly, some sensors comprise a pair of electrodes in electricalcommunication with an environment external to the sensor. Suchelectrical communication may be desirable for allowing the sensor tooutput electrical data indicative of the environment to which it isexposed. For example, some sensors may be configured to output theequivalent surface potential across one or more pairs of electrodestherein. Electrodes may be placed in electrical communication with anenvironment external thereto by, for example, being placed in electricalcommunication with a component in communication with the environmentexternal thereto. This may be accomplished by placing the electrodes indirect contact with the relevant component. In some embodiments, a wirebonding composition is disposed on a portion of an external surface ofthe electrodes described herein for this purpose. The wire bondingcomposition may be configured to also be capable of being placed inelectrical communication with a component capable of outputting datafrom the electrodes in a manner that can easily be interpreted by a userof the sensor and/or computer program (e.g., with a voltmeter).

FIG. 15 shows one example of a sensor comprising a wire bondingcomposition 6022 disposed on a portion of each member of the pair ofelectrodes 122. Example 2 provides more detail about one process thatmay be employed to dispose a wire bonding composition on a pair ofelectrodes. As shown in FIG. 15, the wirebonding composition may bedisposed directly on the electrode material in the electrode. It is alsopossible for the wirebonding composition to be disposed on theelectrodes in a manner such that one or more intervening components arepresent between it and the electrode material. For instance, thewirebonding composition may be disposed on an electrically conductivematerial disposed on the electrode material, such as an electricallyconductive material that facilitates bonding between the electrodematerial and the wirebonding composition. One example of an electricallyconductive material suitable for this purpose is an alloy of titaniumand gold. When the wirebonding composition is disposed directly on aportion of the electrode material in an electrode for which apassivating layer is disposed directly on a different portion thereof,the electrode material in the electrodes may be exposed for contact withthe wirebonding composition by removing a portion of the passivatinglayer disposed thereon. This may be accomplished by, for instance,employing a photolithography technique described elsewhere herein.

Another example of a step that may be performed during the fabricationof the sensors described herein is the formation of one or morecomponents thereof that promotes interaction between the sensor and oneor more analytes of interest in a desirable manner. By way of example,the surface chemistry of one or more components of the sensor may bealtered to promote a desirable interaction with one or more analytes ofinterest (in other words, one or more components of the sensor may befunctionalized). For instance, one or more types of molecules may bebound to the surfaces of a plurality of nanowires. Such molecules mayinclude those which are configured to bind with an analyte of interest(e.g., they may comprise antibodies for an antigen of interest).Molecules of interest may be bound to the nanowires by covalentattachment. In some embodiments, covalent attachment of molecules ofinterest to the nanowires may be facilitated by the use of silanederivatives. A silane derivative comprising a functional group suitablefor bonding with the molecule of interest (e.g., an amino group, such asa primary amino group, an aldehyde group, an epoxy group) may becovalently attached to the nanowires. Then, the molecule(s) of interestmay, after optionally being activated to facilitate bonding with thesilane derivative, allowed to react with the silane derivative to form acovalent bond therewith. In some embodiments, it may be advantageous toalter the surface chemistry of the plurality of nanowires as one of thelater steps during sensor fabrication and/or after steps during whichthe molecule(s) of interest may be degraded (e.g., after anyphotolithography steps, after any etching steps).

As another example, and as also described elsewhere herein, in someembodiments, a blocking layer is formed on one or more components of thesensor. The blocking layer may be positioned between these component(s)and an environment external to the sensor. In some embodiments, ablocking layer mediates interactions between one or more components ofan environment external to the sensor (e.g., one or more samples to beanalyzed and/or one or more components thereof, such as one or moreanalytes therein). For instance, a blocking layer may reducenon-specific interactions of sample(s) and/or component(s) therein withone or more components of the sensor (e.g., with a plurality ofnanowires therein). Blocking layers suitable for this purpose may beformed from and/or comprise materials that do not bind readily withsample components (e.g., proteins) other than the analyte(s) ofinterest. As another example, a blocking layer may reduce electrostaticcharge screening by a sample to be analyzed with one or more componentsof the sensor (e.g., with a plurality of nanowires therein).

A blocking layer may be introduced to a sensor by a variety of suitableprocesses. One example of a suitable process comprises dispensing asolution comprising the components of the blocking layer on the sensorand/or one or more components thereof and then incubating the sensor onwhich the solution is disposed to allow for bonding between thecomponents of the blocking layer and the sensor and/or component(s)thereof.

When present, a blocking layer may be disposed on one or more discreteportions of the sensor or may form a coating that covers a significantfraction of the sensor (e.g., it may cover all, or a majority, of theportions of the sensor not in electrical communication with anenvironment external thereto). FIG. 16 shows one example of a sensor asensor comprising a blocking layer 7024 that is disposed over a nanowireplacing a pair of electrodes 124 in electrical communication, but absentfrom other portions of the sensor.

Some methods may comprise the formation of electrodes other than thepairs of electrodes described elsewhere herein and some sensors maycomprise such electrodes. By way of example, a sensor may furthercomprise a back gate electrode, a water gate electrode, and/or a groundelectrode. These electrode(s), when present, may be formed byphotolithography processes (e.g., as described elsewhere herein). Theymay be performed in a single step or may be fabricated by separatesteps. The steps employed to form these electrode(s) may be performed atany suitable time. In some embodiments, one or more of these electrodesmay be formed concurrently with the formation of the pair(s) ofelectrodes. For instance, a photolithographic process employed to form apair of electrodes as described elsewhere herein may also comprise theformation of one or more further electrodes by also comprising removalof the photoresist from the location at which these electrode(s) are tobe formed concurrently with removal of the photoresist from the locationat which the pair of electrodes is to be formed and by also comprisingdeposition of the material forming these electrode(s) on the portion(s)of the substrate exposed by this process concurrently with deposition ofthe material forming the pair of electrodes.

FIG. 17A shows one non-limiting embodiment of a sensor comprising a pairof electrodes 126 and further comprising a back gate electrode 8026, awater gate electrode 9026, and a ground electrode 10026. Suchelectrodes, when present, may be directly exposed to an environmentexternal to the sensor and/or may lack passivating layers and/orelectrically insulating layers disposed thereon. In other embodiments,one or more passivating layers and/or electrically insulating layers maybe positioned between one or more of these electrodes and an environmentexternal thereto.

In some embodiments, a back gate electrode, a water gate electrode,and/or a ground electrode may be disposed on the substrate such that itis in direct contact with the material forming the bulk thereof (e.g.,instead of the surface layer). By way of example, in some embodiments,an electrode (e.g., a back gate electrode) is deposited onto a portionof the substrate from which the surface layer has been etched. Withoutwishing to be bound by any particular theory, it is believed that it maybe advantageous for back gate electrodes to be disposed on the substratesuch that they are in direct contact with the material forming the bulkthereof. It is believed that this arrangement may enhance theconsistency of the gating provided by the back gate electrode, may allowfor dry gating of the plurality of nanowires, and/or may provide afacile way to ground the bulk substrate.

FIG. 17B shows a top view of one exemplary embodiment of a sensorcomprising two further electrodes in addition to a plurality of pairs ofelectrodes. In FIG. 17B, a plurality of pairs of electrodes 128 iselectrodes arranged to have radial symmetry around a center point. Afirst electrode AA is disposed on and symmetrically around the centerpoint. A second electrode BB is in electrical communication with thefirst electrode AA. Each electrode is in electrical communication withan environment external to the sensor by a wire connecting the electrodewith a contact pad 1328. The contact pad may be placed in electricalcommunication with a voltmeter, computer, or other device. A sensorhaving a design like that shown in FIG. 17B may be configured such thatboth the first and second electrodes are ground electrodes. It is alsopossible for a sensor to have a design like that shown in FIG. 17B andbe configured such that both the first and second electrodes arereference electrodes, or for such a sensor to be configured to employone but not the other of the first and second electrodes shown in FIG.17B. FIG. 17C shows one example of a sensor including the secondelectrode shown in FIG. 17B but not the first electrode. In otherrespects, this sensor is the same as the sensor shown in FIG. 17B.

In some embodiments, a sensor further comprises an external layerconfigured to be removed prior to and/or during use thereof. Theexternal layer may protect the sensor prior to use (e.g., duringtransport) and then removed so that the sensor can function whendesired. In some embodiments, the external layer is a layer that issoluble in a fluid to which the sensor is configured to be exposed(e.g., for the purpose of removing the layer, during sensing). By way ofexample, in some embodiments, the external layer may be a layer that issoluble in buffered saline and/or one or more bodily fluids. Such layersmay be removed by dissolution in the relevant fluid. Non-limitingexamples of suitable compositions for external layers include sugarsand/or proteins.

FIG. 18 shows one non-limiting example of a sensor comprising anexternal layer 11030. As shown in FIG. 18, an external layer may bedisposed on the entirety of the external surface of a sensor. It is alsopossible for a sensor to comprise an external layer that is disposedonly on one or more portions thereof (e.g., one or more particularlydelicate portions, such as nanowires therein and/or molecule(s)configured to bond with one or more analytes of interest exposedthereto) and/or to form a conformal coating.

The sensors described herein may be incorporated into fluidic devices.By way of example, in some embodiments, a fluidic device comprises oneor more sensors described herein. The fluidic device may be configuredto receive a fluid, pass the fluid over the sensor, and then outputinformation about the fluid (e.g., the presence and/or concentration ofone or more analytes) based on a property of the sensor upon exposure tothe fluid. In some embodiments, a fluidic device may comprise aplurality of sensors. The fluidic device may be configured to pass afluid over two or more sensors sequentially (e.g., each sensor may beconfigured to sense a different property of the fluid, such as thepresence and/or concentration of different analytes therein) and/or maycomprise two or more sensors that are not in fluidic communication witheach other (e.g., a fluidic device may comprise multiple, distinct fluidpathways through which fluid can be passed that are each configured toact on a fluid introduced thereto in an identical manner). Some fluidicdevices comprising the sensors described herein may be microfluidicdevices.

Having provided an overview of the various components that may beincluded the sensors described herein and the methods that may beemployed to form the sensors described herein, further details regardingparticular sensor components and method steps are provided below.

As described elsewhere herein, some sensors comprise a plurality ofnanowires. When present, the nanowires may have one or more physical orchemical characteristics that enhance sensor performance. Such physicaland chemical characteristics are described below.

A plurality of nanowires may comprise a variety of suitable numbers ofnanowires. In some embodiments, a plurality of nanowires comprises atleast 30 nanowires, at least 50 nanowires, at least 75 nanowires, atleast 100 nanowires, at least 200 nanowires, at least 500 nanowires, atleast 750 nanowires, at least 1,000 nanowires, at least 1,250 nanowires,at least 1,500 nanowires, at least 1,750 nanowires, at least 2,000nanowires, at least 2,500 nanowires, at least 3,000 nanowires, at least4,000 nanowires, at least 5,000 nanowires, at least 7,500 nanowires, atleast 10,000 nanowires, at least 20,000 nanowires, at least 50,000nanowires, or at least 75,000 nanowires. In some embodiments, aplurality of nanowires comprises at most 100,000 nanowires, at most75,000 nanowires, at most 50,000 nanowires, at most 20,000 nanowires, atmost 10,000 nanowires, at most 7,500 nanowires, at most 5,000 nanowires,at most 4,000 nanowires, at most 3,000 nanowires, at most 2,500nanowires, at most 2,000 nanowires, at most 1,750 nanowires, at most1,500 nanowires, at most 1,250 nanowires, at most 1,000 nanowires, atmost 750 nanowires, at most 500 nanowires, at most 200 nanowires, atmost 100 nanowires, at most 75 nanowires, or at most 50 nanowires.Combinations of the above-referenced ranges are also possible (e.g., atleast 30 nanowires and at most 100,000 nanowires, or at least 30nanowires and at most 1,000 nanowires). Other ranges are also possible.

In some embodiments, a plurality of nanowires comprises nanowiresoriented substantially tangentially to a circular structure. Suchnanowires may have an angle with respect to the circular structure thatis greater than or equal to 70°, greater than or equal to 72.5°, greaterthan or equal to 75°, greater than or equal to 77.5°, greater than orequal to 80°, greater than or equal to 82.5°, greater than or equal to85°, greater than or equal to 87.5°, or greater than or equal to 89°. Insome embodiments, a nanowire that is oriented substantially tangentiallyto a circular structure has an angle with respect to the circularstructure of less than or equal to 90°, less than or equal to 89°, lessthan or equal to 87.5°, less than or equal to 85°, less than or equal to82.5°, less than or equal to 80°, less than or equal to 77.5°, less thanor equal to 75°, or less than or equal to 72.5°. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 70° and less than or equal to 90°, or greater than or equal to 80°and less than or equal to 90°). Other ranges are also possible.

Some pluralities of nanowires may comprise a relatively high number ofnanowires that are oriented substantially tangentially to a circularstructure. For instance, in some embodiments, greater than or equal to30%, greater than or equal to 40%, greater than or equal to 50%, greaterthan or equal to 60%, greater than or equal to 70%, greater than orequal to 75%, greater than or equal to 80%, greater than or equal to85%, greater than or equal to 90%, greater than or equal to 95%, greaterthan or equal to 97.5%, or greater than or equal to 99% of the nanowiresin a plurality of nanowires have an angle with respect to a circularstructure in one or more of the above-referenced ranges. In someembodiments, less than or equal to 100%, less than or equal to 99%, lessthan or equal to 97.5%, less than or equal to 95%, less than or equal to90%, less than or equal to 85%, less than or equal to 80%, less than orequal to 75%, less than or equal to 70%, less than or equal to 60%, lessthan or equal to 50%, or less than or equal to 40% of the nanowires in aplurality of nanowires have an angle with respect to a circularstructure in one or more of the above-referenced ranges. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to 30% and less than or equal to 100%, greater than or equal to75% and less than or equal to 100%). Other ranges are also possible.

In some embodiments, a plurality of nanowires comprises nanowires havinga chemical composition that is desirable. By way of example, thenanowires may be formed from and/or comprise a material that is capableof being functionalized with one or more chemistries of interest (e.g.,one or more chemistries having a desirable interaction with an analyteof interest and/or which can further react with a molecule having adesirable interaction with an analyte of interest). As another example,the nanowires may be formed from and/or comprise a material having adesirable electrical conductivity and/or equivalent surface potential(e.g., from a semiconductor, from a material that exhibits a change inelectrical conductivity upon exposure to an analyte of interest, and/orfrom a material that exhibits a change in equivalent surface potentialupon exposure to an analyte of interest). Non-limiting examples ofmaterials having this property include selected elements (e.g.,silicon), ceramics (e.g., gallium nitride, gallium arsenide, indiumoxide, indium phosphide, molybdenum disulfide, tungsten disulfide),polymers (e.g., semiconducting polymers), one-dimensional materials(e.g., carbon nanotubes, one-dimensional materials comprising one ormore of the above-referenced materials), and two-dimensional materials(e.g., graphene, two-dimensional materials comprising one or more of theabove-referenced materials). In some embodiments, the nanowires areformed from and/or comprise one or more of the above-referencedmaterials in single-crystalline form (e.g., single-crystalline silicon).

Non-limiting examples of functional groups the surfaces of the nanowiresmay be functionalized to include comprise hydroxyl groups, epoxy groups,aldehyde groups, amino groups (e.g., (3-aminopropyl)triethoxysilane),and halogen groups. Some functional groups may cause the nanowires tohave a charged surface (e.g., positively charged, negatively charged,zwitterionic). In some embodiments, a surface of a nanowire isfunctionalized with a binding entity (e.g., a binding entity for ananalyte to be detected by the sensor). By way of example, a nanowire maycomprise a binding entity for glial fibrillary acidic protein (GFAP),UCH-L1, S1000, ICH, NFL-1, D-dimer, a viral protein (e.g., a human viralprotein, a non-human animal viral protein, a plant viral protein), asmall molecule and/or a lipid. Further non-limiting examples of viralproteins include a SARS-CoV-2 proteins (e.g., spike (S) proteins,nucleocapsid (N) proteins, envelope (E) proteins), influenza virusproteins (e.g., hemagglutinin (HA) proteins, neuraminidase (NA)proteins, matrix proteins (M1, M2)), zika virus proteins, parainfluenzavirus proteins, HIV1 proteins, CMV proteins, and HHV proteins.

Some nanowires suitable for use in the sensors described herein have anelectrical conductivity in a desirable range. By way of example, in someembodiments, a plurality of nanowires comprises nanowires having anelectrical conductivity of greater than or equal to 0.333 S/cm, greaterthan or equal to 0.667 S/cm, greater than or equal to 1 S/cm, greaterthan or equal to 2.22 S/cm, greater than or equal to 6.67 S/cm, greaterthan or equal to 10 S/cm, greater than or equal to 12 S/cm, greater thanor equal to 14.3 S/cm, greater than or equal to 20 S/cm, greater than orequal to 50 S/cm, greater than or equal to 75 S/cm, greater than orequal to 100 S/cm, greater than or equal to 200 S/cm, greater than orequal to 286 S/cm, greater than or equal to 350 S/cm, greater than orequal to 500 S/cm, greater than or equal to 750 S/cm, greater than orequal to 1,000 S/cm, greater than or equal to 2,000 S/cm, greater thanor equal to 5,000 S/cm, greater than or equal to 7,500 S/cm, greaterthan or equal to 10,000 S/cm, greater than or equal to 20,000 S/cm,greater than or equal to 30,000 S/cm, or greater than or equal to 40,000S/cm. In some embodiments, a plurality of nanowires comprises nanowireshaving an electrical conductivity of less than or equal to 50,000 S/cm,less than or equal to 40,000 S/cm, less than or equal to 30,000 S/cm,less than or equal to 20,000 S/cm, less than or equal to 10,000 S/cm,less than or equal to 7,500 S/cm, less than or equal to 5,000 S/cm, lessthan or equal to 2,000 S/cm, less than or equal to 1,000 S/cm, less thanor equal to 750 S/cm, less than or equal to 500 S/cm, less than or equalto 350 S/cm, less than or equal to 286 S/cm, less than or equal to 200S/cm, less than or equal to 100 S/cm, less than or equal to 75 S/cm,less than or equal to 50 S/cm, less than or equal to 20 S/cm, less thanor equal to 14.3 S/cm, less than or equal to 12 S/cm, less than or equalto 10 S/cm, less than or equal to 6.67 S/cm, less than or equal to 2.22S/cm, less than or equal to 1 S/cm, or less than or equal to 0.67 S/cm.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 0.333 S/cm and less than or equal to 50,000S/cm, greater than or equal to 2.22 S/cm and less than or equal to 286S/cm, or greater than or equal to 14.3 S/cm and less than or equal to286 S/cm). Other ranges are also possible. The electrical conductivityof a plurality of nanowires may be determined by use of a semiconductorparameter analyzer.

In some embodiments, the average conductivity of the nanowires in aplurality of nanowires is in one or more of the above-referenced ranges.The ranges described above may independently characterize initialconductivity of the nanowires (e.g., the conductivity of the nanowiresat their time of manufacture, the conductivity of the nanowires afterdeposition on a substrate but prior to functionalization, theconductivity of the nanowires after sensor fabrication but before usethereof) and/or the conductivity of the nanowires at another point intime (e.g., after use of the sensor for a period of minutes, hours,days, or longer).

Some nanowires suitable for use in the sensors described herein have anon/off ratio that is advantageous. For instance, a plurality ofnanowires may comprise nanowires having an on/off ratio of greater thanor equal to 2, greater than or equal to 5, greater than or equal to 7.5,greater than or equal to 10, greater than or equal to 20, greater thanor equal to 50, greater than or equal to 75, greater than or equal to100, greater than or equal to 200, greater than or equal to 500, greaterthan or equal to 750, greater than or equal to 1,000, greater than orequal to 2,000, greater than or equal to 5,000, greater than or equal to7,500, greater than or equal to 10,000, greater than or equal to 20,000,greater than or equal to 50,000, greater than or equal to 75,000,greater than or equal to 100,000, greater than or equal to 200,000,greater than or equal to 500,000, or greater than or equal to 750,000.In some embodiments, a plurality of nanowires comprises nanowires havingan on/off ratio of less than or equal to 1,000,000, less than or equalto 750,000, less than or equal to 500,000, less than or equal to200,000, less than or equal to 100,000, less than or equal to 75,000,less than or equal to 50,000, less than or equal to 20,000, less than orequal to 10,000, less than or equal to 7,500, less than or equal to5,000, less than or equal to 2,000, less than or equal to 1,000, lessthan or equal to 750, less than or equal to 500, less than or equal to200, less than or equal to 100, less than or equal to 75, less than orequal to 50, less than or equal to 20, less than or equal to 10, lessthan or equal to 7.5, or less than or equal to 5. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 2 and less than or equal to 1,000,000, greater than or equal to 1,000and less than or equal to 1,000,000, or greater than or equal to 10,000and less than or equal to 1,000,000). Other ranges are also possible.

The on/off ratio for a nanowire may be determined by generating an IVcurve by performing a gate sweep and then determining the ratio of thecurrent when the device is in the “on” state to the current when thedevice is in the “off” state from the IV curve. Briefly, the followingprocedure may be followed: (1) a constant direct current voltage may beapplied across the pair of electrodes; (2) concurrently, the voltageapplied to a gate electrode may be varied from −0.5 V to 0.5 V; (3) thecurrent in the “off” state may be determined to be the minimum currentmeasured during variation of the voltage applied to the gate electrode;(4) the current in the “on” state may be determined to be the maximumcurrent measured during variation of the voltage applied to the gateelectrode; and (5) the on/off ratio may be determined by dividing thecurrent in the “on” state by the current in the “off” state.

In some embodiments, the average on/off ratio of the nanowires in aplurality of nanowires is in one or more of the above-referenced ranges.The ranges described above may independently characterize initial on/offratio of the nanowires (e.g., the on/off ratio of the nanowires at theirtime of manufacture, on/off ratio of the nanowires after deposition on asubstrate but prior to functionalization, on/off ratio of the nanowiresafter sensor fabrication but before use thereof) and/or the on/off ratioof the nanowires at another point in time (e.g., after use of the sensorfor a period of minutes, hours, days, or longer).

The nanowires described herein may have a variety of suitable lengths.In some embodiments, a plurality of nanowires comprises nanowires havinga length of greater than or equal to 4 microns, greater than or equal to5 microns, greater than or equal to 6 microns, greater than or equal to8 microns, greater than or equal to 10 microns, greater than or equal to11 microns, greater than or equal to 12 microns, greater than or equalto 13 microns, greater than or equal to 14 microns, greater than orequal to 15 microns, greater than or equal to 16 microns, greater thanor equal to 17 microns, greater than or equal to 18 microns, greaterthan or equal to 19 microns, greater than or equal to 20 microns,greater than or equal to 22 microns, greater than or equal to 25microns, greater than or equal to 27.5 microns, greater than or equal to30 microns, greater than or equal to 35 microns, greater than or equalto 40 microns, or greater than or equal to 45 microns. In someembodiments, a plurality of nanowires comprises nanowires having alength of less than or equal to 50 microns, less than or equal to 45microns, less than or equal to 40 microns, less than or equal to 35microns, less than or equal to 30 microns, less than or equal to 27.5microns, less than or equal to 25 microns, less than or equal to 22microns, less than or equal to 20 microns, less than or equal to 19microns, less than or equal to 18 microns, less than or equal to 17microns, less than or equal to 16 microns, less than or equal to 15microns, less than or equal to 14 microns, less than or equal to 13microns, less than or equal to 12 microns, less than or equal to 11microns, less than or equal to 10 microns, less than or equal to 8microns, or less than or equal to 6 microns. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 4 microns and less than or equal to 40 microns, greater than or equalto 5 microns and less than or equal to 50 microns, greater than or equalto 10 microns and less than or equal to 25 microns, greater than orequal to 12 microns and less than or equal to 20 microns, or greaterthan or equal to 14 microns and less than or equal to 16 microns). Otherranges are also possible. In some embodiments, the average length of thenanowires in a plurality of nanowires is in one or more of theabove-referenced ranges.

The nanowires described herein may have a variety of suitable diameters.In some embodiments, a plurality of nanowires comprises nanowires havinga diameter of greater than or equal to 12 nm, greater than or equal to13 nm, greater than or equal to 14 nm, greater than or equal to 15 nm,greater than or equal to 16 nm, greater than or equal to 17 nm, greaterthan or equal to 18 nm, greater than or equal to 19 nm, greater than orequal to 20 nm, greater than or equal to 21 nm, greater than or equal to22 nm, greater than or equal to 23 nm, greater than or equal to 24 nm,greater than or equal to 25 nm, greater than or equal to 27 nm, greaterthan or equal to 30 nm, greater than or equal to 32.5 nm, or greaterthan or equal to 35 nm. In some embodiments, a plurality of nanowirescomprises nanowires having a diameter of less than or equal to 40 nm,less than or equal to 35 nm, less than or equal to 32.5 nm, less than orequal to 30 nm, less than or equal to 27 nm, less than or equal to 25nm, less than or equal to 24 nm, less than or equal to 23 nm, less thanor equal to 22 nm, less than or equal to 21 nm, less than or equal to 20nm, less than or equal to 19 nm, less than or equal to 18 nm, less thanor equal to 17 nm, less than or equal to 16 nm, less than or equal to 15nm, less than or equal to 14 nm, or less than or equal to 13 nm.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 12 nm and less than or equal to 40 nm, greaterthan or equal to 15 nm and less than or equal to 25 nm, or greater thanor equal to 19 nm and less than or equal to 21 nm). Other ranges arealso possible. In some embodiments, the average diameter of thenanowires in a plurality of nanowires is in one or more of theabove-referenced ranges.

As described elsewhere herein, in some embodiments, a sensor comprises ablocking layer disposed on a portion thereof, such as on a plurality ofnanowires therein. When present, the blocking layer may comprise apolymeric material, such as a protein (e.g., casein, bovine serumalbumin), an oligosaccharide, a polysaccharide (e.g., carboxymethylcellulose), a synthetic polymer (e.g., poly(vinyl pyrrolidone),poly(ethylene imine), poly(ethylene glycol)), and/or a derivative of theabove-referenced polymers (e.g., an acetylated polymer, such asacetylated bovine serum albumin). In some embodiments, a blocking layerfurther comprises one or more stabilizers, such as a free radicalabsorber (e.g., histidine, a beta-mercaptan, a thiol), a pH stabilizer,and/or a moisture control agent. The stabilizer(s) may increase theshelf-life of the sensor and/or may be configured to be removed uponcontact with a fluid to which the sensor is configured to be exposed,such as buffered saline and/or one or more bodily fluids. For instance,in some embodiments, the stabilizer is configured to be dissolved in afluid to which the sensor is configured to be exposed.

As described elsewhere herein, in some embodiments, a sensor comprisesone or more pairs of electrodes. Further details regarding suchelectrodes are provided below.

The sensors described herein may comprise a variety of suitable numbersof pairs of electrodes (e.g., that are arranged to have radial symmetryabout a center point). In some embodiments, a sensor comprises greaterthan or equal to 5, greater than or equal to 6, greater than or equal to7, greater than or equal to 8, greater than or equal to 9, greater thanor equal to 10, greater than or equal to 11, greater than or equal to12, greater than or equal to 13, greater than or equal to 14, greaterthan or equal to 15, greater than or equal to 16, greater than or equalto 17, greater than or equal to 18, greater than or equal to 19, greaterthan or equal to 20, greater than or equal to 21, greater than or equalto 22, greater than or equal to 23, greater than or equal to 24, greaterthan or equal to 25, greater than or equal to 26, greater than or equalto 27, greater than or equal to 28, greater than or equal to 29, greaterthan or equal to 30, greater than or equal to 31, greater than or equalto 32, greater than or equal to 34, greater than or equal to 36, greaterthan or equal to 38, greater than or equal to 40, or greater than orequal to 45 pairs of electrodes. In some embodiments, a sensor comprisesless than or equal to 50, less than or equal to 45, less than or equalto 40, less than or equal to 38, less than or equal to 36, less than orequal to 34, less than or equal to 32, less than or equal to 31, lessthan or equal to 30, less than or equal to 29, less than or equal to 28,less than or equal to 27, less than or equal to 26, less than or equalto 25, less than or equal to 24, less than or equal to 23, less than orequal to 22, less than or equal to 21, less than or equal to 20, lessthan or equal to 19, less than or equal to 18, less than or equal to 17,less than or equal to 16, less than or equal to 15, less than or equalto 14, less than or equal to 13, less than or equal to 12, less than orequal to 11, less than or equal to 10, less than or equal to 9, lessthan or equal to 8, less than or equal to 7, or less than or equal to 6pairs of electrodes. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to 5 and less than or equalto 50, greater than or equal to 10 and less than or equal to 50, greaterthan or equal to 10 and less than or equal to 40, or greater than orequal to 15 and less than or equal to 25). Other ranges are alsopossible.

The sensors described herein may comprise a variety of suitable numbersof motifs (e.g., comprising pairs of electrodes) that are arranged tohave radial symmetry about a center point. In some embodiments, a sensorcomprises greater than or equal to 2 or greater than or equal to 3motifs. In some embodiments, a sensor comprises less than or equal to 4less than or equal to 3 motifs. Combinations of the above-referencedranges are also possible (e.g., greater than or equal to 2 and less thanor equal to 4. Other ranges are also possible.

In some embodiments, a suitable percentage of the electrode pairs in asensor (e.g., a sensor comprising a plurality of pairs of electrodesthat are arranged to have radial symmetry about a center point) may bein electrical communication by exactly one nanowire. The percentage ofelectrode pairs in communication by exactly one nanowire may be greaterthan or equal to 0%, greater than or equal to 1%, greater than or equalto 2%, greater than or equal to 5%, greater than or equal to 7.5%,greater than or equal to 10%, greater than or equal to 12.5%, greaterthan or equal to 15%, greater than or equal to 17.5%, greater than orequal to 20%, greater than or equal to 22.5%, greater than or equal to25%, greater than or equal to 27.5%, greater than or equal to 30%,greater than or equal to 35%, greater than or equal to 40%, greater thanor equal to 45%, greater than or equal to 50%, greater than or equal to60%, greater than or equal to 70%, greater than or equal to 80%, orgreater than or equal to 90%. In some embodiments, the percentage ofelectrode pairs in communication by exactly one nanowire is less than orequal to 100%, less than or equal to 90%, less than or equal to 80%,less than or equal to 70%, less than or equal to 60%, less than or equalto 50%, less than or equal to 45%, less than or equal to 40%, less thanor equal to 35%, less than or equal to 30%, less than or equal to 27.5%,less than or equal to 25%, less than or equal to 22.5%, less than orequal to 20%, less than or equal to 17.5%, less than or equal to 15%,less than or equal to 12.5%, less than or equal to 10%, less than orequal to 7.5%, less than or equal to 5%, less than or equal to 2%, orless than or equal to 1%. Combinations of the above-referenced rangesare also possible (e.g., greater than or equal to 0% and less than orequal to 100%, greater than or equal to 10% and less than or equal to50%, or greater than or equal to 15% and less than or equal to 25%).Other ranges are also possible.

In some embodiments, a pair of electrodes that is in electricalcommunication by exactly one nanowire is also suitably configured formaking a measurement of an analyte in a fluid as described elsewhereherein. Accordingly, in some embodiments, a sensor may comprise apercentage of pairs of electrodes that are acceptable for sensing in oneor more of the ranges described above.

A sensor may comprise a pair of electrodes in which an inner electrodeis nested inside an outer electrode. Both the inner and the outerelectrode may comprise two connected portions and one portion thatconnects the two connected portions. The connecting portion may placethe two connected portions in electrical communication with each other.The connected portions may be substantially parallel, or may be orientedwith respect to each other in another manner (e.g., the two connectedportions may be oriented radially outwards from a center point). It isalso possible for the connected portions may be substantially straightor to comprise one or more curves, angles, and/or kinks. Similarly, theportion that connects the two connected portions may be substantiallystraight or may comprise one or more curves, angles, and/or kinks. Byway of example, in some embodiments, a portion that connects twoconnected portions may comprise three sub-portions, each of which aresubstantially straight.

FIG. 19 shows one example of a pair of electrodes comprising oneelectrode including a connecting portion comprising three sub-portions.In FIG. 19, the outer electrode 30 comprises connected portions 30A and30B. It further comprises a connecting portion 30C comprising thesubportions 30C₁, 30C₂, and 30C₃. FIG. 19 also shows an inner electrode40 that comprises connected portions 40A and 40B, and further comprisesa connecting portion 40C that is substantially straight. In embodimentslike FIG. 19, in which an inner electrode comprises a connecting portionthat is substantially straight and an outer electrode comprises aconnecting portion that comprises three subportions, the lengths of theconnected portions for the inner electrode may be substantially the sameas those for the outer electrode (e.g., their lengths may be within 5%,2%, or 1% of each other). As also shown in FIG. 19, the connectedportions of the inner and outer electrodes that are adjacent to eachother may be substantially parallel. With reference to FIG. 19, theconnected portion 40A of the inner electrode 40 is substantiallyparallel to the connected portion 30A of the outer electrode 30 and theconnected portion of 40B of the inner electrode 40 is substantiallyparallel to the connected portion 30B of the outer electrode 30.

It should be noted that, when a pair of electrodes comprises an innerelectrode and an outer electrode, either electrode may be the sourceelectrode and either electrode may be the drain electrode.

The dimensions of each portion of the electrode may generally beselected as desired. In some embodiments, an outer electrode (e.g., anelectrode comprising connected portions positioned around connectedportions of an inner electrode) comprises connected portions having alength of greater than or equal to 100 microns, greater than or equal to125 microns, greater than or equal to 150 microns, greater than or equalto 175 microns, greater than or equal to 200 microns, greater than orequal to 225 microns, greater than or equal to 250 microns, greater thanor equal to 275 microns, greater than or equal to 300 microns, greaterthan or equal to 325 microns, greater than or equal to 344 microns,greater than or equal to 375 microns, greater than or equal to 400microns, greater than or equal to 450 microns, greater than or equal to500 microns, greater than or equal to 600 microns, or greater than orequal to 800 microns. In some embodiments, an outer electrode comprisesconnected portions having a length of less than or equal to 1,000microns, less than or equal to 800 microns, less than or equal to 600microns, less than or equal to 500 microns, less than or equal to 450microns, less than or equal to 400 microns, less than or equal to 375microns, less than or equal to 344 microns, less than or equal to 325microns, less than or equal to 300 microns, less than or equal to 275microns, less than or equal to 250 microns, less than or equal to 225microns, less than or equal to 200 microns, less than or equal to 175microns, less than or equal to 150 microns, or less than or equal to 125microns. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 100 microns and less than or equal to1,000 microns, or greater than or equal to 300 and less than or equal to400 microns). Other ranges are also possible.

Two connected portions of an outer electrode may have substantially thesame length (e.g., they may have lengths within 5%, 2%, or 1% of eachother) or may have lengths that differ from each other. When a pair ofconnected portions of an outer electrode have different lengths, eachsuch electrode portion may independently have a length in one or more ofthe ranges described above.

In some embodiments, an outer electrode (e.g., an electrode comprisingconnected portions positioned around the connected portions of an innerelectrode) comprises connected portions having a width of greater thanor equal to 1 micron, greater than or equal to 1.5 microns, greater thanor equal to 2 microns, greater than or equal to 2.5 microns, greaterthan or equal to 3 microns, greater than or equal to 3.5 microns,greater than or equal to 4 microns, greater than or equal to 4.5microns, greater than or equal to 5 microns, greater than or equal to5.5 microns, greater than or equal to 6 microns, greater than or equalto 6.5 microns, greater than or equal to 7 microns, greater than orequal to 7.5 microns, greater than or equal to 8 microns, greater thanor equal to 9 microns, greater than or equal to 10 microns, greater thanor equal to 15 microns, greater than or equal to 20 microns, greaterthan or equal to 50 microns, greater than or equal to 75 microns,greater than or equal to 100 microns, greater than or equal to 150microns, greater than or equal to 200 microns, or greater than or equalto 250 microns. In some embodiments, an outer electrode comprisesconnected portions having a width of less than or equal to 300 microns,less than or equal to 250 microns, less than or equal to 200 microns,less than or equal to 150 microns, less than or equal to 100 microns,less than or equal to 75 microns, less than or equal to 50 microns, lessthan or equal to 20 microns, less than or equal to 15 microns, less thanor equal to 10 microns, less than or equal to 9 microns, less than orequal to 8 microns, less than or equal to 7.5 microns, less than orequal to 7 microns, less than or equal to 6.5 microns, less than orequal to 6 microns, less than or equal to 5.5 microns, less than orequal to 5 microns, less than or equal to 4.5 microns, less than orequal to 4 microns, less than or equal to 3.5 microns, less than orequal to 3 microns, less than or equal to 2.5 microns, less than orequal to 2 microns, or less than or equal to 1.5 microns. Combinationsof the above-referenced ranges are also possible (e.g., greater than orequal to 1 micron and less than or equal to 300 microns, or greater thanor equal to 3 and less than or equal to 7 microns). Other ranges arealso possible.

Two connected portions of an outer electrode may have substantially thesame width (e.g., they may have widths within 10%, 5%, 2%, or 1% of eachother) or may have widths that differ from each other. When a pair ofconnected portions of an outer electrode have different widths, eachsuch electrode portion may independently have a width in one or more ofthe ranges described above. It should also be understood that the valueslisted above may independently describe the average width of theconnected portions of the outer electrode or the median width of theconnected portions of the outer electrode.

In some embodiments, an outer electrode (e.g., an electrode comprisingconnected portions positioned around the connected portions of an innerelectrode) comprises connected portions having a height of greater thanor equal to 0.05 microns, greater than or equal to 0.01 micron, greaterthan or equal to 0.02 microns, greater than or equal to 0.05 microns,greater than or equal to 0.075 microns, greater than or equal to 0.1micron, greater than or equal to 0.15 microns, greater than or equal to0.175 microns, greater than or equal to 0.2 microns, greater than orequal to 0.225 microns, greater than or equal to 0.25 microns, greaterthan or equal to 0.275 microns, greater than or equal to 0.3 microns,greater than or equal to 0.325 microns, greater than or equal to 0.35microns, greater than or equal to 0.375 microns, greater than or equalto 0.4 microns, or greater than or equal to 0.45 microns. In someembodiments, an outer electrode comprises connected portions having aheight of less than or equal to 0.5 microns, less than or equal to 0.45microns, less than or equal to 0.4 microns, less than or equal to 0.375microns, less than or equal to 0.35 microns, less than or equal to 0.325microns, less than or equal to 0.3 microns, less than or equal to 0.275microns, less than or equal to 0.25 microns, less than or equal to 0.225microns, less than or equal to 0.2 microns, less than or equal to 0.175microns, less than or equal to 0.15 microns, less than or equal to 0.1micron, less than or equal to 0.075 microns, less than or equal to 0.05microns, less than or equal to 0.02 microns, or less than or equal to0.01 micron. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 0.05 microns and less than orequal to 0.5 microns, or greater than or equal to 0.15 microns and lessthan or equal to 0.35 microns). Other ranges are also possible.

Two connected portions of an outer electrode may have substantially thesame height (e.g., they may have heights within 10%, 5%, 2%, or 1% ofeach other) or may have heights that differ from each other. When a pairof connected portions of an outer electrode have different heights, eachsuch electrode portion may independently have a height in one or more ofthe ranges described above. It should also be understood that the valueslisted above may independently describe the average height of theconnected portions of the outer electrode or the median height of theconnected portions of the outer electrode.

A portion of an outer electrode (e.g., an electrode comprising connectedportions positioned around the connected portions of an inner electrode)connecting two connected portions thereof may have a length of greaterthan or equal to 50 microns, greater than or equal to 52 microns,greater than or equal to 55 microns, greater than or equal to 57microns, greater than or equal to 60 microns, greater than or equal to62 microns, greater than or equal to 65 microns, greater than or equalto 67 microns, greater than or equal to 70 microns, greater than orequal to 72 microns, greater than or equal to 75 microns, or greaterthan or equal to 77 microns. In some embodiments, a portion of an outerelectrode connecting two connected portions thereof has a length of lessthan or equal to 80 microns, less than or equal to 77 microns, less thanor equal to 75 microns, less than or equal to 72 microns, less than orequal to 70 microns, less than or equal to 67 microns, less than orequal to 65 microns, less than or equal to 62 microns, less than orequal to 60 microns, less than or equal to 57 microns, less than orequal to 55 microns, less than or equal to 52 microns, or less than orequal to 50 microns. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to 50 microns and less thanor equal to 80 microns, or greater than or equal to 60 microns and lessthan or equal to 67 microns). Other ranges are also possible.

It should also be understood that the values listed above mayindependently describe the length of a connecting portion of an outerelectrode from one end to the other, the spacing between the connectedportions of the outer electrode, the length of the longest portion ofthe connecting portion, and/or the length of the connecting portionoriented at the largest angle to the connected portions.

A portion of an outer electrode (e.g., an electrode comprising connectedportions positioned around the connected portions of an inner electrode)connecting two connected portions thereof may have a width of greaterthan or equal to 5 microns, greater than or equal to 6 microns, greaterthan or equal to 7 microns, greater than or equal to 8 microns, greaterthan or equal to 9 microns, greater than or equal to 10 microns, greaterthan or equal to 11 microns, greater than or equal to 12 microns,greater than or equal to 13 microns, or greater than or equal to 14microns. In some embodiments, a portion of an outer electrode connectingtwo connected portions thereof has a width of less than or equal to 15microns, less than or equal to 14 microns, less than or equal to 13microns, less than or equal to 12 microns, less than or equal to 11microns, less than or equal to 10 microns, less than or equal to 9microns, less than or equal to 8 microns, less than or equal to 7microns, or less than or equal to 6 microns. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 5 microns and less than or equal to 10 microns). Other ranges arealso possible.

It should also be understood that the values listed above mayindependently describe the average width of a portion of the outerelectrode connecting two connected portions thereof or the median widthof the portion of the outer electrode connecting two connected portionsthereof.

A portion of an outer electrode (e.g., an electrode comprising connectedportions positioned around the connected portions of an inner electrode)connecting two connected portions thereof may have a height of greaterthan or equal to 0.005 microns, greater than or equal to greater than orequal to 0.0075 microns, greater than or equal to 0.01 micron, greaterthan or equal to 0.02 microns, greater than or equal to 0.05 microns,greater than or equal to 0.075 microns, greater than or equal to 0.1micron, greater than or equal to 0.15 microns, greater than or equal to0.175 microns, greater than or equal to 0.2 microns, greater than orequal to 0.225 microns, greater than or equal to 0.25 microns, greaterthan or equal to 0.275 microns, greater than or equal to 0.3 microns,greater than or equal to 0.325 microns, greater than or equal to 0.35microns, greater than or equal to 0.375 microns, greater than or equalto 0.4 microns, or greater than or equal to 0.45 microns. In someembodiments, a portion of an outer electrode connecting two connectedportions thereof has a height of less than or equal to 0.5 microns, lessthan or equal to 0.45 microns, less than or equal to 0.4 microns, lessthan or equal to 0.375 microns, less than or equal to 0.35 microns, lessthan or equal to 0.325 microns, less than or equal to 0.3 microns, lessthan or equal to 0.275 microns, less than or equal to 0.25 microns, lessthan or equal to 0.225 microns, less than or equal to 0.2 microns, lessthan or equal to 0.175 microns, less than or equal to 0.15 microns, lessthan or equal to 0.1 micron, less than or equal to 0.075 microns, lessthan or equal to 0.05 microns, less than or equal to 0.02 microns, lessthan or equal to 0.01 micron, or less than or equal to 0.0075 microns.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 0.005 microns and less than or equal to 0.5microns, greater than or equal to 0.05 microns and less than or equal to0.5 microns, or greater than or equal to 0.15 microns and less than orequal to 0.35 microns). Other ranges are also possible.

It should also be understood that the values listed above mayindependently describe the average height of a portion of the outerelectrode connecting two connected portions thereof or the median heightof the portion of the outer electrode connecting two connected portionsthereof.

In some embodiments, an inner electrode (e.g., an electrode comprisingconnected portions positioned between the connected portions of an outerelectrode) comprises connected portions having a length of greater thanor equal to 100 microns, greater than or equal to 125 microns, greaterthan or equal to 150 microns, greater than or equal to 175 microns,greater than or equal to 200 microns, greater than or equal to 225microns, greater than or equal to 250 microns, greater than or equal to275 microns, greater than or equal to 300 microns, greater than or equalto 325 microns, greater than or equal to 344 microns, greater than orequal to 375 microns, greater than or equal to 400 microns, greater thanor equal to 450 microns, greater than or equal to 500 microns, greaterthan or equal to 600 microns, or greater than or equal to 800 microns.In some embodiments, an inner electrode comprises connected portionshaving a length of less than or equal to 1,000 microns, less than orequal to 800 microns, less than or equal to 600 microns, less than orequal to 500 microns, less than or equal to 450 microns, less than orequal to 400 microns, less than or equal to 375 microns, less than orequal to 344 microns, less than or equal to 325 microns, less than orequal to 300 microns, less than or equal to 275 microns, less than orequal to 250 microns, less than or equal to 225 microns, less than orequal to 200 microns, less than or equal to 175 microns, less than orequal to 150 microns, or less than or equal to 125 microns. Combinationsof the above-referenced ranges are also possible (e.g., greater than orequal to 100 microns and less than or equal to 1,000 microns, or greaterthan or equal to 300 and less than or equal to 400 microns). Otherranges are also possible.

Two connected portions of an inner electrode may have substantially thesame length (e.g., they may have lengths within 5%, 2%, or 1% of eachother) or may have lengths that differ from each other. When a pair ofconnected portions of an inner electrode have different lengths, eachsuch electrode portion may independently have a length in one or more ofthe ranges described above.

In some embodiments, an inner electrode (e.g., an electrode comprisingconnected portions positioned between the connected portions of an outerelectrode) comprises connected portions having a width of greater thanor equal to 1 micron, greater than or equal to 1.5 microns, greater thanor equal to 2 microns, greater than or equal to 2.5 microns, greaterthan or equal to 3 microns, greater than or equal to 3.5 microns,greater than or equal to 4 microns, greater than or equal to 4.5microns, greater than or equal to 5 microns, greater than or equal to5.5 microns, greater than or equal to 6 microns, greater than or equalto 6.5 microns, greater than or equal to 7 microns, greater than orequal to 7.5 microns, greater than or equal to 8 microns, greater thanor equal to 9 microns, greater than or equal to 10 microns, greater thanor equal to 15 microns, greater than or equal to 20 microns, greaterthan or equal to 50 microns, greater than or equal to 75 microns,greater than or equal to 100 microns, greater than or equal to 150microns, greater than or equal to 200 microns, or greater than or equalto 250 microns. In some embodiments, an inner electrode comprisesconnected portions having a width of less than or equal to 300 microns,less than or equal to 250 microns, less than or equal to 200 microns,less than or equal to 150 microns, less than or equal to 100 microns,less than or equal to 75 microns, less than or equal to 50 microns, lessthan or equal to 20 microns, less than or equal to 15 microns, less thanor equal to 10 microns, less than or equal to 9 microns, less than orequal to 8 microns, less than or equal to 7.5 microns, less than orequal to 7 microns, less than or equal to 6.5 microns, less than orequal to 6 microns, less than or equal to 5.5 microns, less than orequal to 5 microns, less than or equal to 4.5 microns, less than orequal to 4 microns, less than or equal to 3.5 microns, less than orequal to 3 microns, less than or equal to 2.5 microns, less than orequal to 2 microns, or less than or equal to 1.5 microns. Combinationsof the above-referenced ranges are also possible (e.g., greater than orequal to 1 micron and less than or equal to 300 microns, or greater thanor equal to 3 microns and less than or equal to 7 microns). Other rangesare also possible.

Two connected portions of an inner electrode may have substantially thesame width (e.g., they may have widths within 5%, 2%, or 1% of eachother) or may have widths that differ from each other. When a pair ofconnected portions of an inner electrode have different widths, eachsuch electrode portion may independently have a width in one or more ofthe ranges described above. It should also be understood that the valueslisted above may independently describe the average width of theconnected portions of the inner electrode or the median width of theconnected portions of the inner electrode.

In some embodiments, an inner electrode (e.g., an electrode comprisingconnected portions positioned between the connected portions of an outerelectrode) comprises connected portions having a height of greater thanor equal to 0.05 microns, greater than or equal to 0.01 micron, greaterthan or equal to 0.02 microns, greater than or equal to 0.05 microns,greater than or equal to 0.075 microns, greater than or equal to 0.1micron, greater than or equal to 0.15 microns, greater than or equal to0.175 microns, greater than or equal to 0.2 microns, greater than orequal to 0.225 microns, greater than or equal to 0.25 microns, greaterthan or equal to 0.275 microns, greater than or equal to 0.3 microns,greater than or equal to 0.325 microns, greater than or equal to 0.35microns, greater than or equal to 0.375 microns, greater than or equalto 0.4 microns, or greater than or equal to 0.45 microns. In someembodiments, an inner electrode comprises connected portions having aheight of less than or equal to 0.5 microns, less than or equal to 0.45microns, less than or equal to 0.4 microns, less than or equal to 0.375microns, less than or equal to 0.35 microns, less than or equal to 0.325microns, less than or equal to 0.3 microns, less than or equal to 0.275microns, less than or equal to 0.25 microns, less than or equal to 0.225microns, less than or equal to 0.2 microns, less than or equal to 0.175microns, less than or equal to 0.15 microns, less than or equal to 0.1micron, less than or equal to 0.075 microns, less than or equal to 0.05microns, less than or equal to 0.02 microns, or less than or equal to0.01 micron. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 0.05 microns and less than orequal to 0.5 microns, or greater than or equal to 0.15 microns and lessthan or equal to 0.35 microns). Other ranges are also possible.

Two connected portions of an inner electrode may have substantially thesame height (e.g., they may have heights within 10%, 5%, 2%, or 1% ofeach other) or may have heights that differ from each other. When a pairof connected portions of an inner electrode have different heights, eachsuch electrode portion may independently have a height in one or more ofthe ranges described above. It should also be understood that the valueslisted above may independently describe the average height of theconnected portions of the inner electrode or the median height of theconnected portions of the inner electrode.

A portion of an inner electrode (e.g., an electrode comprising connectedportions positioned between the connected portions of an outerelectrode) connecting two connected portions thereof may have a lengthof greater than or equal to 40 microns, greater than or equal to 41microns, greater than or equal to 42 microns, greater than or equal to43 microns, greater than or equal to 44 microns, greater than or equalto 45 microns, greater than or equal to 46 microns, greater than orequal to 47 microns, greater than or equal to 48 microns, greater thanor equal to 49 microns, greater than or equal to 50 microns, greaterthan or equal to 51 microns, greater than or equal to 52 microns,greater than or equal to 53 microns, or greater than or equal to 54microns. In some embodiments, a portion of an inner electrode connectingtwo connected portions thereof has a length of less than or equal to 55microns, less than or equal to 54 microns, less than or equal to 53microns, less than or equal to 52 microns, less than or equal to 51microns, less than or equal to 50 microns, less than or equal to 49microns, less than or equal to 48 microns, less than or equal to 47microns, less than or equal to 46 microns, less than or equal to 45microns, less than or equal to 44 microns, less than or equal to 43microns, less than or equal to 42 microns, or less than or equal to 41microns. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 40 microns and less than or equal to 50microns, or greater than or equal to 45 microns and less than or equalto 55 microns). Other ranges are also possible.

It should also be understood that the values listed above mayindependently describe the length of a connecting portion of an innerelectrode from one end to the other, the spacing between the connectedportions of the inner electrode, the length of the longest portion ofthe connecting portion, and/or the length of the connecting portionoriented at the largest angle with the connected portions.

A portion of an inner electrode (e.g., an electrode comprising connectedportions positioned between the connected portions of an outerelectrode) connecting two connected portions thereof may have a width ofgreater than or equal to 1 micron, greater than or equal to 1.5 microns,greater than or equal to 2 microns, greater than or equal to 2.5microns, greater than or equal to 3 microns, greater than or equal to3.5 microns, greater than or equal to 4 microns, greater than or equalto 4.5 microns, greater than or equal to 5 microns, greater than orequal to 5.5 microns, greater than or equal to 6 microns, greater thanor equal to 6.5 microns, greater than or equal to 7 microns, greaterthan or equal to 7.5 microns, greater than or equal to 8 microns,greater than or equal to 9 microns, greater than or equal to 10 microns,greater than or equal to 15 microns, greater than or equal to 20microns, greater than or equal to 50 microns, greater than or equal to75 microns, greater than or equal to 100 microns, greater than or equalto 150 microns, greater than or equal to 200 microns, or greater than orequal to 250 microns. In some embodiments, a portion of an innerelectrode connecting two connected portions thereof has a width of lessthan or equal to 300 microns, less than or equal to 250 microns, lessthan or equal to 200 microns, less than or equal to 150 microns, lessthan or equal to 100 microns, less than or equal to 75 microns, lessthan or equal to 50 microns, less than or equal to 20 microns, less thanor equal to 15 microns, less than or equal to 10 microns, less than orequal to 9 microns, less than or equal to 8 microns, less than or equalto 7.5 microns, less than or equal to 7 microns, less than or equal to6.5 microns, less than or equal to 6 microns, less than or equal to 5.5microns, less than or equal to 5 microns, less than or equal to 4.5microns, less than or equal to 4 microns, less than or equal to 3.5microns, less than or equal to 3 microns, less than or equal to 2.5microns, less than or equal to 2 microns, or less than or equal to 1.5microns. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 1 micron and less than or equal to 300microns, or greater than or equal to 3 and less than or equal to 7microns). Other ranges are also possible.

It should also be understood that the values listed above mayindependently describe the average width of a portion of the innerelectrode connecting two connected portions thereof or the median widthof the portion of the inner electrode connecting two connected portionsthereof.

A portion of an inner electrode (e.g., an electrode comprising connectedportions positioned between the connected portions of an outerelectrode) connecting two connected portions thereof may have a heightof greater than or equal to 0.005 microns, greater than or equal togreater than or equal to 0.0075 microns, greater than or equal to 0.01micron, greater than or equal to 0.02 microns, greater than or equal to0.05 microns, greater than or equal to 0.075 microns, greater than orequal to 0.1 micron, greater than or equal to 0.15 microns, greater thanor equal to 0.175 microns, greater than or equal to 0.2 microns, greaterthan or equal to 0.225 microns, greater than or equal to 0.25 microns,greater than or equal to 0.275 microns, greater than or equal to 0.3microns, greater than or equal to 0.325 microns, greater than or equalto 0.35 microns, greater than or equal to 0.375 microns, greater than orequal to 0.4 microns, or greater than or equal to 0.45 microns. In someembodiments, a portion of an inner electrode connecting two connectedportions thereof has a height of less than or equal to 0.5 microns, lessthan or equal to 0.45 microns, less than or equal to 0.4 microns, lessthan or equal to 0.375 microns, less than or equal to 0.35 microns, lessthan or equal to 0.325 microns, less than or equal to 0.3 microns, lessthan or equal to 0.275 microns, less than or equal to 0.25 microns, lessthan or equal to 0.225 microns, less than or equal to 0.2 microns, lessthan or equal to 0.175 microns, less than or equal to 0.15 microns, lessthan or equal to 0.1 micron, less than or equal to 0.075 microns, lessthan or equal to 0.05 microns, less than or equal to 0.02 microns, lessthan or equal to 0.01 micron, or less than or equal to 0.0075 microns.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 0.05 microns and less than or equal to 0.5microns, or greater than or equal to 0.15 microns and less than or equalto 0.35 microns). Other ranges are also possible.

It should also be understood that the values listed above mayindependently describe the average height of a portion of the innerelectrode connecting two connected portions thereof or the median heightof the portion of the inner electrode connecting two connected portionsthereof.

When a pair of electrodes comprises an outer electrode and an innerelectrode, the spacing therebetween may be selected as desired. In someembodiments, the distance between one of the connected portions of anouter electrode and the connected portion of the inner electrode towhich it is closest (e.g., the distance between portions 30A and 40A inFIG. 19, or the distance between portions 30B and 40B in FIG. 19) isgreater than or equal to 1 micron, greater than or equal to 1.25microns, greater than or equal to 1.5 microns, greater than or equal to1.75 microns, greater than or equal to 2 microns, greater than or equalto 2.25 microns, greater than or equal to 2.5 microns, greater than orequal to 3 microns, greater than or equal to 3.5 microns, greater thanor equal to 4 microns, greater than or equal to 5 microns, greater thanor equal to 6 microns, greater than or equal to 7 microns, greater thanor equal to 8 microns, greater than or equal to 8.5 microns, greaterthan or equal to 9 microns, greater than or equal to 9.25 microns,greater than or equal to 9.5 microns, greater than or equal to 9.75microns, greater than or equal to 10 microns, greater than or equal to10.5 microns, greater than or equal to 11 microns, greater than or equalto 11.5 microns, greater than or equal to 12 microns, greater than orequal to 12.5 microns, greater than or equal to 13 microns, greater thanor equal to 13.5 microns, greater than or equal to 14 microns, greaterthan or equal to 15 microns, greater than or equal to 17.5 microns,greater than or equal to 20 microns, greater than or equal to 25microns, greater than or equal to 30 microns, greater than or equal to35 microns, or greater than or equal to 40 microns. In some embodiments,the distance between one of the connected portions of an outer electrodeand the connected portion of the inner electrode to which it is closestis less than or equal to 50 microns, less than or equal to 40 microns,less than or equal to 35 microns, less than or equal to 25 microns, lessthan or equal to 20 microns, less than or equal to 17.5 microns, lessthan or equal to 15 microns, less than or equal to 14 microns, less thanor equal to 13.5 microns, less than or equal to 13 microns, less than orequal to 12.5 microns, less than or equal to 12 microns, less than orequal to 11.5 microns, less than or equal to 11 microns, less than orequal to 10.5 microns, less than or equal to 10 microns, less than orequal to 9.75 microns, less than or equal to 9.5 microns, less than orequal to 9.25 microns, less than or equal to 9 microns, less than orequal to 8.5 microns, less than or equal to 8 microns, less than orequal to 7 microns, less than or equal to 6 microns, less than or equalto 5 microns, less than or equal to 4 microns, less than or equal to 3.5microns, less than or equal to 3 microns, less than or equal to 2.5microns, less than or equal to 2.25 microns, less than or equal to 2microns, less than or equal to 1.75 microns, less than or equal to 1.5microns, or less than or equal to 1.25 microns. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 1 micron and less than or equal to 50 microns, greater than or equalto 1.5 microns and less than or equal to 12 microns, greater than orequal to 5 microns and less than or equal to 15 microns, or greater thanor equal to 9 microns and less than or equal to 10 microns). Otherranges are also possible.

It should also be understood that the values listed above mayindependently describe the average distance between one of the connectedportions of an outer electrode and the connected portion of the innerelectrode to which it is closest, the median distance between one of theconnected portions of an outer electrode and the connected portion ofthe inner electrode to which it is closest, or the minimum distancebetween one of the connected portions of an outer electrode and theconnected portion of the inner electrode to which it is closest.

In some embodiments, the distance between one of the connected portionsof an outer electrode and the connected portion of the inner electrodeto which it is closest may be relatively close to the length of ananowire placing the inner and outer electrodes in electricalcommunication. In some embodiments, the ratio of the length of thenanowire to the distance between one of the connected portions of anouter electrode and the connected portion of the inner electrode towhich it is closest is greater than or equal to 1, greater than or equalto 1.5, greater than or equal to 2, greater than or equal to 2.5,greater than or equal to 3, greater than or equal to 3.5, greater thanor equal to 4, or greater than or equal to 4.5. In some embodiments, theratio of the length of the nanowire to the distance between one of theconnected portions of an outer electrode and the connected portion ofthe inner electrode to which it is closest is less than or equal to 5,less than or equal to 4.5, less than or equal to 4, less than or equalto 3.5, less than or equal to 3, less than or equal to 2.5, less than orequal to 2, or less than or equal to 1.5. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 1 and less than or equal to 5). Other ranges are also possible.

It should also be understood that the ratios listed above mayindependently describe the ratio of the length of the nanowire to theaverage distance between one of the connected portions of an outerelectrode and the connected portion of the inner electrode to which itis closest, the ratio of the length of the nanowire to the mediandistance between one of the connected portions of an outer electrode andthe connected portion of the inner electrode to which it is closest, orthe ratio of the length of the nanowire to the minimum distance betweenone of the connected portions of an outer electrode and the connectedportion of the inner electrode to which it is closest.

As described elsewhere herein, in some embodiments, a pair of electrodescomprises two electrodes that are straight and parallel to each other(e.g., they may have a structure like that shown in FIG. 1) and/or aplurality of electrodes comprises an array of electrodes that arestraight and parallel to each other.

The dimensions of electrodes that are straight and parallel to eachother may generally be selected as desired. In some embodiments, such anelectrode comprises has a length of greater than or equal to 100microns, greater than or equal to 125 microns, greater than or equal to150 microns, greater than or equal to 175 microns, greater than or equalto 200 microns, greater than or equal to 225 microns, greater than orequal to 250 microns, greater than or equal to 275 microns, greater thanor equal to 300 microns, greater than or equal to 325 microns, greaterthan or equal to 344 microns, greater than or equal to 375 microns,greater than or equal to 400 microns, greater than or equal to 450microns, greater than or equal to 500 microns, greater than or equal to600 microns, or greater than or equal to 800 microns. In someembodiments, a straight electrode has a length of less than or equal to1,000 microns, less than or equal to 800 microns, less than or equal to600 microns, less than or equal to 500 microns, less than or equal to450 microns, less than or equal to 400 microns, less than or equal to375 microns, less than or equal to 344 microns, less than or equal to325 microns, less than or equal to 300 microns, less than or equal to275 microns, less than or equal to 250 microns, less than or equal to225 microns, less than or equal to 200 microns, less than or equal to175 microns, less than or equal to 150 microns, or less than or equal to125 microns. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 100 microns and less than orequal to 1,000 microns, or greater than or equal to 300 and less than orequal to 400 microns). Other ranges are also possible.

Straight and parallel electrodes may have substantially the same length(e.g., they may have lengths within 5%, 2%, or 1% of each other) or mayhave lengths that differ from each other. When a plurality of straightand parallel electrodes comprises electrodes having different lengths,each such electrode may independently have a length in one or more ofthe ranges described above.

In some embodiments, a straight electrode has a width of greater than orequal to 1 micron, greater than or equal to 1.5 microns, greater than orequal to 2 microns, greater than or equal to 2.5 microns, greater thanor equal to 3 microns, greater than or equal to 3.5 microns, greaterthan or equal to 4 microns, greater than or equal to 4.5 microns,greater than or equal to 5 microns, greater than or equal to 5.5microns, greater than or equal to 6 microns, greater than or equal to6.5 microns, greater than or equal to 7 microns, greater than or equalto 7.5 microns, greater than or equal to 8 microns, greater than orequal to 9 microns, greater than or equal to 10 microns, greater than orequal to 15 microns, greater than or equal to 20 microns, greater thanor equal to 50 microns, greater than or equal to 75 microns, greaterthan or equal to 100 microns, greater than or equal to 150 microns,greater than or equal to 200 microns, or greater than or equal to 250microns. In some embodiments, a straight electrode has a width of lessthan or equal to 300 microns, less than or equal to 250 microns, lessthan or equal to 200 microns, less than or equal to 150 microns, lessthan or equal to 100 microns, less than or equal to 75 microns, lessthan or equal to 50 microns, less than or equal to 20 microns, less thanor equal to 15 microns, less than or equal to 10 microns, less than orequal to 9 microns, less than or equal to 8 microns, less than or equalto 7.5 microns, less than or equal to 7 microns, less than or equal to6.5 microns, less than or equal to 6 microns, less than or equal to 5.5microns, less than or equal to 5 microns, less than or equal to 4.5microns, less than or equal to 4 microns, less than or equal to 3.5microns, less than or equal to 3 microns, less than or equal to 2.5microns, less than or equal to 2 microns, or less than or equal to 1.5microns. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 1 micron and less than or equal to 300microns, or greater than or equal to 3 and less than or equal to 7microns). Other ranges are also possible.

Straight and parallel electrodes may have substantially the same width(e.g., they may have widths within 5%, 2%, or 1% of each other) or mayhave widths that differ from each other. When a plurality of straightand parallel electrodes comprises electrodes having different widths,each such electrode may independently have a width in one or more of theranges described above.

In some embodiments, a straight electrode has a height of greater thanor equal to 0.05 microns, greater than or equal to 0.01 micron, greaterthan or equal to 0.02 microns, greater than or equal to 0.05 microns,greater than or equal to 0.075 microns, greater than or equal to 0.1micron, greater than or equal to 0.15 microns, greater than or equal to0.175 microns, greater than or equal to 0.2 microns, greater than orequal to 0.225 microns, greater than or equal to 0.25 microns, greaterthan or equal to 0.275 microns, greater than or equal to 0.3 microns,greater than or equal to 0.325 microns, greater than or equal to 0.35microns, greater than or equal to 0.375 microns, greater than or equalto 0.4 microns, or greater than or equal to 0.45 microns. In someembodiments, a straight electrode has a height of less than or equal to0.5 microns, less than or equal to 0.45 microns, less than or equal to0.4 microns, less than or equal to 0.375 microns, less than or equal to0.35 microns, less than or equal to 0.325 microns, less than or equal to0.3 microns, less than or equal to 0.275 microns, less than or equal to0.25 microns, less than or equal to 0.225 microns, less than or equal to0.2 microns, less than or equal to 0.175 microns, less than or equal to0.15 microns, less than or equal to 0.1 micron, less than or equal to0.075 microns, less than or equal to 0.05 microns, less than or equal to0.02 microns, or less than or equal to 0.01 micron. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 0.05 microns and less than or equal to 0.5 microns, or greater thanor equal to 0.15 microns and less than or equal to 0.35 microns). Otherranges are also possible.

Straight and parallel electrodes may have substantially the same height(e.g., they may have heights within 5%, 2%, or 1% of each other) or mayhave heights that differ from each other. When a plurality of straightand parallel electrodes comprises electrodes having different heights,each such electrode may independently have a height in one or more ofthe ranges described above.

In some embodiments, the distance between straight and parallelelectrodes is greater than or equal to 1 micron, greater than or equalto 1.25 microns, greater than or equal to 1.5 microns, greater than orequal to 1.75 microns, greater than or equal to 2 microns, greater thanor equal to 2.25 microns, greater than or equal to 2.5 microns, greaterthan or equal to 3 microns, greater than or equal to 3.5 microns,greater than or equal to 4 microns, greater than or equal to 5 microns,greater than or equal to 6 microns, greater than or equal to 7 microns,greater than or equal to 8 microns, greater than or equal to 8.5microns, greater than or equal to 9 microns, greater than or equal to9.25 microns, greater than or equal to 9.5 microns, greater than orequal to 9.75 microns, greater than or equal to 10 microns, greater thanor equal to 10.5 microns, greater than or equal to 11 microns, greaterthan or equal to 11.5 microns, greater than or equal to 12 microns,greater than or equal to 12.5 microns, greater than or equal to 13microns, greater than or equal to 13.5 microns, greater than or equal to14 microns, greater than or equal to 15 microns, greater than or equalto 17.5 microns, greater than or equal to 20 microns, greater than orequal to 25 microns, greater than or equal to 30 microns, greater thanor equal to 35 microns, or greater than or equal to 40 microns. In someembodiments, the distance between straight and parallel electrodes isless than or equal to 50 microns, less than or equal to 40 microns, lessthan or equal to 35 microns, less than or equal to 25 microns, less thanor equal to 20 microns, less than or equal to 17.5 microns, less than orequal to 15 microns, less than or equal to 14 microns, less than orequal to 13.5 microns, less than or equal to 13 microns, less than orequal to 12.5 microns, less than or equal to 12 microns, less than orequal to 11.5 microns, less than or equal to 11 microns, less than orequal to 10.5 microns, less than or equal to 10 microns, less than orequal to 9.75 microns, less than or equal to 9.5 microns, less than orequal to 9.25 microns, less than or equal to 9 microns, less than orequal to 8.5 microns, less than or equal to 8 microns, less than orequal to 7 microns, less than or equal to 6 microns, less than or equalto 5 microns, less than or equal to 4 microns, less than or equal to 3.5microns, less than or equal to 3 microns, less than or equal to 2.5microns, less than or equal to 2.25 microns, less than or equal to 2microns, less than or equal to 1.75 microns, less than or equal to 1.5microns, or less than or equal to 1.25 microns. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 1 micron and less than or equal to 50 microns, greater than or equalto 1.5 microns and less than or equal to 12 microns, greater than orequal to 5 microns and less than or equal to 15 microns, or greater thanor equal to 9 microns and less than or equal to 10 microns). Otherranges are also possible.

Pairs of nearest neighbor straight and parallel electrodes may havesubstantially the same distance therebetween (e.g., they may have beseparated by distances within 5%, 2%, or 1% of each other) or may beseparated by distances that differ from each other. When a plurality ofstraight and parallel electrodes comprises electrodes pairs of nearestneighbor electrodes separated by different distances, each nearestneighbor distance may independently be in one or more of the rangesdescribed above.

In some embodiments, the distance between two straight and parallelelectrodes may be relatively close to the length of a nanowire placingthem in electrical communication. In some embodiments, the ratio of thelength of the nanowire to the distance two straight and parallelelectrodes is greater than or equal to 1, greater than or equal to 1.5,greater than or equal to 2, greater than or equal to 2.5, greater thanor equal to 3, greater than or equal to 3.5, greater than or equal to 4,or greater than or equal to 4.5. In some embodiments, the ratio of thelength of the nanowire to the distance between two straight and parallelelectrodes is less than or equal to 5, less than or equal to 4.5, lessthan or equal to 4, less than or equal to 3.5, less than or equal to 3,less than or equal to 2.5, less than or equal to 2, or less than orequal to 1.5. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 1 and less than or equal to 5).Other ranges are also possible.

The electrodes described herein may comprise and/or be formed from avariety of suitable materials. By way of example, in some embodiments,one or more electrodes described herein comprises and/or is formed froma metal. Non-limiting examples of suitable metals include nickel, gold,aluminum, titanium, and platinum.

As described elsewhere herein, in some embodiments, a passivation layeris disposed on at least a portion of an electrode surface. When present,a passivation layer may have a variety of suitable thicknesses. In someembodiments, a passivation layer disposed on an electrode has athickness of greater than or equal to 300 nm, greater than or equal to325 nm, greater than or equal to 350 nm, greater than or equal to 375nm, greater than or equal to 400 nm, greater than or equal to 425 nm,greater than or equal to 450 nm, greater than or equal to 475 nm,greater than or equal to 500 nm, greater than or equal to 525 nm,greater than or equal to 550 nm, or greater than or equal to 575 nm. Insome embodiments, a passivation layer disposed on an electrode has athickness of less than or equal to 600 nm, less than or equal to 575 nm,less than or equal to 550 nm, less than or equal to 525 nm, less than orequal to 500 nm, less than or equal to 475 nm, less than or equal to 450nm, less than or equal to 425 nm, less than or equal to 400 nm, lessthan or equal to 375 nm, less than or equal to 350 nm, or less than orequal to 325 nm. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 300 nm and less than or equalto 600 nm). Other ranges are also possible. The thickness of thepassivation layer may be determined by ellipsometry.

The passivation layers described herein may comprise and/or be formedfrom a variety of suitable materials. By way of example, in someembodiments, a passivation layer disposed on an electrode comprisesand/or is formed from a polymer and/or a ceramic. Non-limiting examplesof suitable such materials include photoresists (e.g., an AZ seriesphotoresist, an S1800 series photoresist, an SU8 photoresist, a Futurrexphotoresist, a polyimide photoresist, a polyimide-based photoresist),nitrides (e.g., silicon nitride), oxides (e.g., silicon oxide), andsilicates (e.g., tetraethyl orthosilicate).

As also described elsewhere herein, in some embodiments, a wire bondingcomposition is disposed on at least a portion of an electrode surface.The wire bonding composition may facilitate bonding of the electrodewith one or more wires (e.g., wire(s) placing the electrode inelectrical communication with an environment external to the sensor).Suitable wire bonding compositions may comprise and/or be formed from ametal, such as titanium and/or gold.

As described elsewhere herein, some sensors may comprise furtherelectrodes in addition to one or more pairs of electrodes. In someembodiments, one or more of the pair(s) of electrodes in a sensor areconfigured to sense an analyte of interest and one or more further pairsof electrodes are also included in the sensor to provide a functionother than sensing the analyte. Such electrodes are described in furtherdetail below.

In some embodiments, a sensor comprises a water gate electrode. Thewater gate electrode may assist with regulation of the potential of thefluid to which the one or more of the pairs of electrodes are exposed.Advantageously, the water gate electrode may place the fluid at apotential that facilitates an interaction of the fluid with the pair(s)of electrodes that enhances the sensitivity of the sensor to one or moreanalytes therein. By way of example, the water gate electrode may placethe fluid at a potential that enhances its charge sensitivity. In someembodiments, the water gate electrode's utility is enhanced when thewater gate electrode is in direct contact with the fluid comprising theanalyte(s) to be detected. Accordingly, in some embodiments, a watergate electrode is configured to directly contact a fluid to be analyzedby the sensor and/or directly contacts a fluid to be analyzed by thesensor at one or more points in time (e.g., during use of the sensor).

When present, the water gate electrode may have a variety of suitabledesigns. In some embodiments, the water gate electrode is circularand/or has a circular cross-section (e.g., it may be cylindrical). Thewater gate electrode may have a variety of suitable thicknesses. In someembodiments, the water gate electrode has a thickness of greater than orequal to 100 microns, greater than or equal to 150 microns, greater thanor equal to 200 microns, greater than or equal to 250 microns, greaterthan or equal to 300 microns, greater than or equal to 350 microns,greater than or equal to 400 microns, or greater than or equal to 450microns. In some embodiments, the water gate electrode has a thicknessof less than or equal to 500 microns, less than or equal to 450 microns,less than or equal to 400 microns, less than or equal to 350 microns,less than or equal to 300 microns, less than or equal to 250 microns,less than or equal to 200 microns, or less than or equal to 150 microns.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 100 microns and less than or equal to 500microns). Other ranges are also possible.

It should also be understood that the values listed above mayindependently describe the average thickness of a water gate electrodeor the median thickness of the water gate electrode.

A variety of suitable compositions may be employed to form water gateelectrodes. In some embodiments, a water gate electrode comprises and/oris formed from a composition comprising silver, gold, and/or platinum.For instance, a water gate electrode may comprise and/or be formed fromsilver and/or silver chloride. In some embodiments, a water gateelectrode is formed by applying an epoxy ink and/or paste comprisingsilver and silver chloride directly onto a plasma-etched substrate. Asanother example, an epoxy ink and/or paste comprising silver and silverchloride may be applied to an electrode comprising gold to facilitateelectrical communication with a wire bonding pad.

In some embodiments, a sensor comprises a ground electrode. The groundelectrode may be configured to electrically ground a fluid to which thesensor is exposed. This may be advantageous in sensors in which it ispossible that the fluid may overcharge. The ground electrode may be inelectrical communication with a ground wire. In some embodiments, theground electrode is also configured to be in electrical communicationwith a fluid to be analyzed by the sensor under certain conditions(e.g., when the fluid is overcharged). This may be accomplished byplacing the fluid in direct contact with the ground electrode.

A variety of suitable compositions may be employed to form groundelectrodes. In some embodiments, a ground electrode comprises and/or isformed from a metal. For instance, a water gate electrode may compriseand/or be formed from gold and/or platinum.

In some embodiments, a sensor comprises a back gate electrode. The backgate electrode may be configured to provide a solid state gating of ananowire placing a pair of electrodes in electrical communication.Varying the potential of the back gate electrode may, e.g., vary theconductivity of the nanowire. Advantageously, this may allow thesensitivity of the sensor to the analyte to be varied.

A variety of suitable compositions may be employed to form back gateelectrodes. In some embodiments, a back gate electrode comprises and/oris formed from a metal or a semiconductor. For instance, a water gateelectrode may comprise and/or be formed from gold and/or silicon (e.g.,doped silicon).

As also described elsewhere herein, in some embodiments, a sensorcomprises an electrically insulating layer. The electrically insulatinglayer may isolate one or more portions of the sensor from direct contactwith an environment external thereto (e.g., it may electrically isolateone or more portions of an electrode surface from a fluid to which thesensor is exposed).

When present, an electrically insulating layer may have a variety ofsuitable thicknesses. In some embodiments, an electrically insulatinglayer has a thickness of greater than or equal to 0.1 micron, greaterthan or equal to 0.2 microns, greater than or equal to 0.5 microns,greater than or equal to 0.75 microns, greater than or equal to 1micron, greater than or equal to 1.1 microns, greater than or equal to1.2 microns, greater than or equal to 1.3 microns, greater than or equalto 1.4 microns, greater than or equal to 1.5 microns, greater than orequal to 1.6 microns, greater than or equal to 1.7 microns, greater thanor equal to 1.8 microns, greater than or equal to 1.9 microns, greaterthan or equal to 2 microns, greater than or equal to 2.1 microns,greater than or equal to 2.2 microns, greater than or equal to 2.5microns, greater than or equal to 2.75 microns, greater than or equal to3 microns, greater than or equal to 5 microns, greater than or equal to10 microns, greater than or equal to 20 microns, greater than or equalto 50 microns, greater than or equal to 75 microns, greater than orequal to 100 microns, greater than or equal to 200 microns, greater thanor equal to 500 microns, greater than or equal to 750 microns, orgreater than or equal to 1,000 microns. In some embodiments, anelectrically insulating layer has a thickness of less than or equal to2,000 microns, less than or equal to 1,000 microns, less than or equalto 750 microns, less than or equal to 500 microns, less than or equal to200 microns, less than or equal to 100 microns, less than or equal to 75microns, less than or equal to 50 microns, less than or equal to 20microns, less than or equal to 10 microns, less than or equal to 5microns, less than or equal to 3 microns, less than or equal to 2.75microns, less than or equal to 2.5 microns, less than or equal to 2.2microns, less than or equal to 2.1 microns, less than or equal to 2microns, less than or equal to 1.9 microns, less than or equal to 1.8microns, less than or equal to 1.7 microns, less than or equal to 1.6microns, less than or equal to 1.5 microns, less than or equal to 1.4microns, less than or equal to 1.3 microns, less than or equal to 1.2microns, less than or equal to 1.1 microns, less than or equal to 1micron, less than or equal to 0.75 microns, less than or equal to 0.5microns, or less than or equal to 0.2 microns. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 0.1 micron and less than or equal to 200 microns, greater than orequal to 0.2 microns and less than or equal to 200 microns, greater thanor equal to 1 micron and less than or equal to 2 microns, or greaterthan or equal to 1.4 microns and less than or equal to 1.6 microns).Other ranges are also possible.

It should also be understood that the values listed above mayindependently describe the average thickness of an electricallyinsulating layer or the median height of the electrically insulatinglayer.

In some embodiments, an electrically insulating layer is positioned suchthat the leakage current between a pair of electrodes and/or between anelectrode in a pair of electrodes and a reference electrode (e.g., awater gate electrode) is less than 3*10⁻¹¹ A.

Electrically insulating layers may, when present, comprise a photoresist(e.g., an AZ series photoresist, an S1800 series photoresist, an SU8photoresist, a Futurrex photoresist). The photoresists suitable for usein forming an electrically insulating layer may also be suitable forperforming the photolithographic processes described elsewhere herein(e.g., those used to form electrodes, passivating layers, wire bondingcompositions, etc. at desired positions). It is also possible for somephotoresists suitable for use in an electrically insulating layer and/orfor photolithography to be biocompatible (e.g., in some embodiments,antibodies, such as IgG, exposed thereto do not undergo excessivedenaturation as determined by ELISA) and/or chemically inert (e.g., insome embodiments, a photoresist does not undergo appreciable changes inhydrophobicity as determined by a water contact angle measurement,diffraction of light, and/or thickness during further sensor fabricationsteps and/or upon exposure to a fluid to be analyzed by the sensor).Advantageously, a suitable photoresist may be readily adherent to one ormore other components of the sensor (e.g., a surface layer, a anelectrode, a passivating layer) in the absence of an adhesion promoter(e.g., in the absence of hexamethyldisilane). Suitable adhesion may beadhesion such that the photoresist does not delaminate from the relevantcomponent(s) during fabrication and/or use of the sensor.

As described above, in some embodiments, a sensor comprises a substrate.One or more other components of the sensor may be disposed thereon.Non-limiting examples of suitable substrates include substratescomprising silicon, silicon oxide, glass, quartz, and/or sapphire. Insome embodiments, the substrate may be a wafer comprising and/or formedfrom one or more of the above-referenced materials. The substrate mayhave a resistivity that is relatively low. For instance, in someembodiments, a sensor is disposed on a substrate having a resistivity ofless than 0.005 ohm-cm.

As also described above, in some embodiments, a surface layer may bedisposed on a substrate. The surface layer may allow for the formationof fiducial alignment marks by etching away a portion thereof and/or mayprovide a suitable surface for the formation of further sensorcomponents thereon.

The surface layers described herein may have a variety of suitablethicknesses. In some embodiments, a surface layer has a thickness ofgreater than or equal to 50 nm, greater than or equal to 75 nm, greaterthan or equal to 100 nm, greater than or equal to 150 nm, greater thanor equal to 200 nm, greater than or equal to 250 nm, greater than orequal to 300 nm, greater than or equal to 350 nm, greater than or equalto 400 nm, greater than or equal to 500 nm, greater than or equal to 600nm, greater than or equal to 700 nm, greater than or equal to 800 nm,greater than or equal to 900 nm, greater than or equal to 1 micron,greater than or equal to 1.25 microns, greater than or equal to 1.5microns, or greater than or equal to 1.75 microns. In some embodiments,a surface layer has a thickness of less than or equal to 2 microns, lessthan or equal to 1.75 microns, less than or equal to 1.5 microns, lessthan or equal to 1.25 microns, less than or equal to 1 micron, less thanor equal to 900 nm, less than or equal to 800 nm, less than or equal to700 nm, less than or equal to 600 nm, less than or equal to 500 nm, lessthan or equal to 400 nm, less than or equal to 350 nm, less than orequal to 300 nm, less than or equal to 250 nm, less than or equal to 200nm, less than or equal to 150 nm, less than or equal to 100 nm, or lessthan or equal to 75 nm. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to 50 nm and less than orequal to 2 microns, greater than or equal to 300 nm and less than orequal to 1 micron, or greater than or equal to 300 nm and less than orequal to 600 nm). Other ranges are also possible.

It should also be understood that the values listed above mayindependently describe the average thickness of a surface layer or themedian thickness of the surface layer.

The surface layers described herein may have a variety of suitablecompositions. By way of example, one or more of the following types oflayers disposed on a substrate: a layer comprising an oxide (e.g., alayer comprising silicon dioxide, such as a layer comprising silicondioxide formed by a wet thermal process and/or a silicon dioxide layerformed by a dry thermal process; a layer comprising aluminum oxide; alayer comprising hafnium oxide; a layer comprising germanium oxide)and/or a layer comprising a nitride (e.g., a layer comprising siliconnitride).

As described elsewhere herein, in some embodiments, a plurality ofnanowires are deposited onto a substrate from a fluid. Further detailsof this process are described below.

Nanowires may be deposited from a variety of suitable fluids. Ingeneral, it may be advantageous for the components of the fluid otherthan the nanowires to be relatively non-toxic. It may also beadvantageous for components of the fluid designed not to be incorporatedinto the sensor (e.g., components other than the nanowires and/orcomponents to be included with the nanowires) to be relatively volatileat the temperature at which the nanowires are deposited therefrom. Insome embodiments, a fluid comprises a liquid, such as an organic solventand/or water. The organic solvent may be an alcohol (e.g., ethanol,isopropanol) and/or an alkane (e.g., hexane). In some embodiments, thefluid further comprises a surfactant, such as a non-ionic surfactant(e.g., Tween 20). One example of a suitable fluid is a fluid comprising1 wt %/vol Tween 20 in deionized water.

Suitable liquids for depositing nanowires may have a relatively lowboiling point. In some embodiments, the liquid has a boiling point ofless than or equal to 120° C., less than or equal to 115° C., less thanor equal to 110° C., less than or equal to 105° C., less than or equalto 100° C., less than or equal to 95° C., less than or equal to 90° C.,less than or equal to 85° C., less than or equal to 80° C., less than orequal to 75° C., less than or equal to 70° C., less than or equal to 65°C., less than or equal to 60° C., or less than or equal to 55° C. Insome embodiments, the liquid has a boiling point of greater than orequal to 50° C., greater than or equal to 55° C., greater than or equalto 60° C., greater than or equal to 65° C., greater than or equal to 70°C., greater than or equal to 75° C., greater than or equal to 80° C.,greater than or equal to 85° C., greater than or equal to 90° C.,greater than or equal to 95° C., greater than or equal to 100° C.,greater than or equal to 105° C., greater than or equal to 110° C., orgreater than or equal to 115° C. Combinations of the above-referencedranges are also possible (e.g., less than or equal to 120° C. andgreater than or equal to 50° C., or less than or equal to 80° C. andgreater than or equal to 50° C.). Other ranges are also possible. Theboiling point of a liquid may be determined by distillation.

In some embodiments, a liquid from which nanowires are deposited has anadvantageous value of specific gravity. For instance, the specificgravity may be greater than or equal to 0.7 g/cm³, greater than or equalto 0.75 g/cm³, greater than or equal to 0.8 g/cm³, greater than or equalto 0.85 g/cm³, greater than or equal to 0.9 g/cm³, greater than or equalto 0.95 g/cm³, greater than or equal to 1 g/cm³, or greater than orequal to 1.05 g/cm³. In some embodiments, the specific gravity is lessthan or equal to 1.1 g/cm³, less than or equal to 1.05 g/cm³, less thanor equal to 1 g/cm³, less than or equal to 0.95 g/cm³, less than orequal to 0.9 g/cm³, less than or equal to 0.85 g/cm³, less than or equalto 0.8 g/cm³, or less than or equal to 0.75 g/cm³. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 0.75 g/cm³ and less than or equal to 1.1 g/cm³). Other ranges arealso possible.

When a plurality of nanowires is deposited onto a substrate from afluid, the nanowires may be present in the fluid in a variety ofsuitable manners. By way of example, the nanowires may be suspended inthe fluid and/or may, together with the other components of the fluid(e.g., together with any water, organic solvents, and/or surfactantstherein), form a colloid. The concentration of the nanowires in thefluid may generally be selected as desired. In some embodiments, a fluidcomprises nanowires at a concentration such that the nanowires have anabsorbance at 420 nm of greater than or equal to 0.45, greater than orequal to 0.46, greater than or equal to 0.47, greater than or equal to0.48, greater than or equal to 0.49, greater than or equal to 0.5,greater than or equal to 0.51, greater than or equal to 0.52, greaterthan or equal to 0.53, or greater than or equal to 0.54. In someembodiments, a fluid comprises nanowires at a concentration such thatthe nanowires have an absorbance at 420 nm of less than or equal to0.55, less than or equal to 0.54, less than or equal to 0.53, less thanor equal to 0.52, less than or equal to 0.51, less than or equal to 0.5,less than or equal to 0.49, less than or equal to 0.48, less than orequal to 0.47, or less than or equal to 0.46. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 0.45 and less than or equal to 0.55). Other ranges are also possible.The absorbance of the nanowires in the fluid may be determined with theuse of a spectrophotometer.

Prior to depositing the fluid on a substrate, the fluid may undergo oneor more processes to enhance the uniformity with which the nanowires aredispersed therein and/or to break up any clumps and/or aggregates ofnanowires therein. This may be accomplished by, for instance, sonicatingthe fluid. The fluid may be sonicated for a variety of suitable amountsof time. In some embodiments, a fluid comprising nanowires is sonicatedfor greater than or equal to 1.5 minutes, greater than or equal to 1.75minutes, greater than or equal to 2 minutes, greater than or equal to2.25 minutes, greater than or equal to 2.5 minutes, greater than orequal to 2.75 minutes, greater than or equal to 3 minutes, greater thanor equal to 3.5 minutes, greater than or equal to 4 minutes, or greaterthan or equal to 4.5 minutes. In some embodiments, a fluid comprisingnanowires is sonicated for less than or equal to 5 minutes, less than orequal to 4.5 minutes, less than or equal to 4 minutes, less than orequal to 3.5 minutes, less than or equal to 3 minutes, less than orequal to 2.75 minutes, less than or equal to 2.5 minutes, less than orequal to 2.25 minutes, less than or equal to 2 minutes, or less than orequal to 1.75 minutes. Combinations of the above-referenced ranges arealso possible (e.g., greater than or equal to 1.5 minutes and less thanor equal to 5 minutes). Other ranges are also possible.

A fluid comprising nanowires may deposit nanowires therefrom from aquantity of fluid having a variety of suitable initial volumes. In someembodiments, the quantity of fluid has an initial volume of greater thanor equal to 0.05 microliters, greater than or equal to 0.075microliters, greater than or equal to 0.1 microliter, greater than orequal to 0.125 microliters, greater than or equal to 0.15 microliters,greater than or equal to 0.175 microliters, greater than or equal to 0.2microliters, greater than or equal to 0.225 microliters, greater than orequal to 0.25 microliters, greater than or equal to 0.275 microliters,greater than or equal to 0.3 microliters, greater than or equal to 0.35microliters, greater than or equal to 0.4 microliters, greater than orequal to 0.5 microliters, greater than or equal to 0.6 microliters, orgreater than or equal to 0.8 microliters. In some embodiments, thequantity of fluid has an initial volume of less than or equal to 1microliter, less than or equal to 0.8 microliters, less than or equal to0.6 microliters, less than or equal to 0.5 microliters, less than orequal to 0.4 microliters, less than or equal to 0.35 microliters, lessthan or equal to 0.3 microliters, less than or equal to 0.275microliters, less than or equal to 0.25 microliters, less than or equalto 0.225 microliters, less than or equal to 0.2 microliters, less thanor equal to 0.175 microliters, less than or equal to 0.15 microliters,less than or equal to 0.125 microliters, less than or equal to 0.1microliter, or less than or equal to 0.075 microliters. Combinations ofthe above-referenced ranges are also possible (e.g., greater than orequal to 0.05 microliters and less than or equal to 1 microliter,greater than or equal to 0.1 microliter and less than or equal to 1microliter, greater than or equal to 0.1 microliter and less than orequal to 0.3 microliters, or greater than or equal to 0.2 microlitersand less than or equal to 0.25 microliters). Other ranges are alsopossible.

As described elsewhere herein, a method may comprise expelling a fluidcomprising a plurality of nanowires onto a substrate to form a quantityof the fluid disposed on the substrate, allowing at least a portion ofthe fluid to evaporate, and replenishing at least a portion of theevaporated fluid. As used herein, the initial volume of the quantity offluid is the maximum volume of the quantity of fluid prior to anyreplenishment of fluid evaporated therefrom. In other words, it is thevolume of the quantity of fluid after it has been fully formed byexpulsion of the fluid onto the substrate and prior to any evaporationthereafter.

When a fluid comprising nanowires is allowed to evaporate from asurface, it may do so over a variety of suitable amounts of time. Insome embodiments, a fluid comprising nanowires is allowed to evaporatefrom a surface over a period of time of greater than or equal to 0.05seconds, greater than or equal to 0.075 seconds, greater than or equalto 0.1 second, greater than or equal to 0.125 seconds, greater than orequal to 0.15 seconds, greater than or equal to 0.175 seconds, greaterthan or equal to 0.2 seconds, greater than or equal to 0.225 seconds,greater than or equal to 0.25 seconds, greater than or equal to 0.275seconds, greater than or equal to 0.3 seconds, greater than or equal to0.325 seconds, greater than or equal to 0.35 seconds, greater than orequal to 0.375 seconds, greater than or equal to 0.4 seconds, greaterthan or equal to 0.45 seconds, greater than or equal to 0.5 seconds,greater than or equal to 0.55 seconds, greater than or equal to 0.6seconds, greater than or equal to 0.8 seconds, greater than or equal to1 second, greater than or equal to 1.5 seconds, greater than or equal to2 seconds, greater than or equal to 2.5 seconds, greater than or equalto 3 seconds, or greater than or equal to 4 seconds. In someembodiments, a fluid comprising nanowires is allowed to evaporate from asurface over a period of time of less than or equal to 5 seconds, lessthan or equal to 4 seconds, less than or equal to 3 seconds, less thanor equal to 2.5 seconds, less than or equal to 2 seconds, less than orequal to 1.5 seconds, less than or equal to 1 second, less than or equalto 0.8 seconds, less than or equal to 0.6 seconds, less than or equal to0.55 seconds, less than or equal to 0.5 seconds, less than or equal to0.45 seconds, less than or equal to 0.4 seconds, less than or equal to0.375 seconds, less than or equal to 0.35 seconds, less than or equal to0.325 seconds, less than or equal to 0.3 seconds, less than or equal to0.275 seconds, less than or equal to 0.25 seconds, less than or equal to0.225 seconds, less than or equal to 0.2 seconds, less than or equal to0.175 seconds, less than or equal to 0.15 seconds, less than or equal to0.125 seconds, less than or equal to 0.1 second, or less than or equalto 0.075 seconds. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 0.05 seconds and less than orequal to 5 seconds, greater than or equal to 0.1 second and less than orequal to 0.5 seconds, or greater than or equal to 0.2 seconds and lessthan or equal to 0.3 seconds). Other ranges are also possible.

When evaporating from a substrate, the contact angle of a fluidcomprising a plurality of nanowires may have a variety of suitablevalues. In some embodiments, the fluid has a contact angle of greaterthan or equal to 20°, greater than or equal to 25°, greater than orequal to 30°, greater than or equal to 35°, greater than or equal to40°, greater than or equal to 45°, greater than or equal to 50°, greaterthan or equal to 55°, greater than or equal to 60°, greater than orequal to 65°, greater than or equal to 70°, greater than or equal to75°, greater than or equal to 80°, or greater than or equal to 85°. Insome embodiments, the fluid has a contact angle of less than or equal to90°, less than or equal to 85°, less than or equal to 80°, less than orequal to 75°, less than or equal to 70°, less than or equal to 65°, lessthan or equal to 60°, less than or equal to 55°, less than or equal to50°, less than or equal to 45°, less than or equal to 40°, less than orequal to 35°, less than or equal to 30°, or less than or equal to 25°.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 20° and less than or equal to 90°). Otherranges are also possible. The contact angle may be measured using agoniometer.

It should be understood that the contact angle of a fluid comprisingnanowires may vary as it evaporates. Accordingly, it should beunderstood that a fluid comprising nanowires may independently have acontact angle in one or more of the above ranges at different points intime during evaporation and/or may have contact angles in two or moredifferent ranges at different points in time during evaporation. By wayof the example, an evaporating fluid may have an initial contact anglein one or more of the above-referenced ranges (e.g., a contact angle atthe point in time described above with respect to initial volume), acontact angle at one or more points in time during evaporation in one ormore of the above-referenced ranges, a contact angle at one or morepoints in time during replenishment in one or more of theabove-referenced ranges, and/or an average contact angle duringevaporation and replenishment in one or more of the above-referencedranges.

As also described elsewhere herein, a fluid comprising nanowires may bedeposited onto a substrate from a nozzle. The nozzle may be positionedat a variety of suitable distances from the substrate during evaporationand/or replenishment of the fluid. In some embodiments, the nozzle ispositioned at a distance of greater than or equal to 0.01 mm, greaterthan or equal to 0.015 mm, greater than or equal to 0.02 mm, greaterthan or equal to 0.025 mm, greater than or equal to 0.03 mm, greaterthan or equal to 0.035 mm, greater than or equal to 0.04 mm, greaterthan or equal to 0.045 mm, greater than or equal to 0.0475 mm, greaterthan or equal to 0.05 mm, greater than or equal to 0.0525 mm, greaterthan or equal to 0.055 mm, greater than or equal to 0.0575 mm, greaterthan or equal to 0.06 mm, greater than or equal to 0.0625 mm, greaterthan or equal to 0.065 mm, greater than or equal to 0.07 mm, greaterthan or equal to 0.08 mm, greater than or equal to 0.09 mm, greater thanor equal to 0.1 mm, greater than or equal to 0.125 mm, greater than orequal to 0.15 mm, greater than or equal to 0.175 mm, greater than orequal to 0.2 mm, or greater than or equal to 0.25 mm from the substrate.In some embodiments, the nozzle is positioned at a distance of less thanor equal to 0.3 mm, less than or equal to 0.25 mm, less than or equal to0.2 mm, less than or equal to 0.175 mm, less than or equal to 0.15 mm,less than or equal to 0.125 mm, less than or equal to 0.1 mm, less thanor equal to 0.09 mm, less than or equal to 0.08 mm, less than or equalto 0.07 mm, less than or equal to 0.065 mm, less than or equal to 0.0625mm, less than or equal to 0.06 mm, less than or equal to 0.0575 mm, lessthan or equal to 0.055 mm, less than or equal to 0.0525 mm, less than orequal to 0.05 mm, less than or equal to 0.0475 mm, less than or equal to0.045 mm, less than or equal to 0.04 mm, less than or equal to 0.035 mm,less than or equal to 0.03 mm, less than or equal to 0.025 mm, less thanor equal to 0.02 mm, or less than or equal to 0.015 mm from thesubstrate. Combinations of the above-referenced ranges are also possible(e.g., greater than or equal to 0.01 mm and less than or equal to 0.3mm, greater than or equal to 0.01 mm and less than or equal to 0.2 mm,greater than or equal to 0.03 mm and less than or equal to 0.1 mm, orgreater than or equal to 0.05 mm and less than or equal to 0.06 mm).Other ranges are also possible.

When a fluid is deposited onto a substrate, the substrate may be held ata variety of suitable temperatures. In some embodiments, the substrateis held at a temperature that facilitates evaporation of the fluid(e.g., the substrate may be heated). The temperature of the substratemay be greater than or equal to 55° C., greater than or equal to 56° C.,greater than or equal to 57° C., greater than or equal to 58° C.,greater than or equal to 59° C., greater than or equal to 60° C.,greater than or equal to 61° C., greater than or equal to 62° C.,greater than or equal to 63° C., greater than or equal to 64° C.,greater than or equal to 65° C., greater than or equal to 66° C.,greater than or equal to 67° C., greater than or equal to 68° C.,greater than or equal to 69° C., greater than or equal to 70° C.,greater than or equal to 71° C., greater than or equal to 72° C.,greater than or equal to 73° C., greater than or equal to 74° C.,greater than or equal to 75° C., greater than or equal to 76° C.,greater than or equal to 77° C., greater than or equal to 78° C., orgreater than or equal to 79° C. The temperature of the substrate may beless than or equal to 80° C., less than or equal to 79° C., less than orequal to 78° C., less than or equal to 77° C., less than or equal to 76°C., less than or equal to 75° C., less than or equal to 74° C., lessthan or equal to 73° C., less than or equal to 72° C., less than orequal to 71° C., less than or equal to 70° C., less than or equal to 69°C., less than or equal to 68° C., less than or equal to 67° C., lessthan or equal to 66° C., less than or equal to 65° C., less than orequal to 64° C., less than or equal to 63° C., less than or equal to 62°C., less than or equal to 61° C., less than or equal to 60° C., lessthan or equal to 59° C., less than or equal to 58° C., less than orequal to 57° C., or less than or equal to 56° C. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 55° C. and less than or equal to 80° C., greater than or equal to 60°C. and less than or equal to 70° C., or greater than or equal to 64° C.and less than or equal to 66° C.). Other ranges are also possible. Thetemperature of the substrate may be determined by a thermocouplepositioned on the surface of the substrate on which the fluid isdeposited.

As described elsewhere herein, in some embodiments, a sensor beingfabricated is heated during fabrication to assist with the formation ofohmic contacts between the electrodes and the nanowires therein. Furtherdetails of this process are described below.

Some embodiments may comprise exposing a sensor being fabricated to atemperature of greater than or equal to 380° C., greater than or equalto 382.5° C., greater than or equal to 385° C., greater than or equal to387.5° C., greater than or equal to 390° C., greater than or equal to392.5° C., greater than or equal to 395° C., greater than or equal to397.5° C., greater than or equal to 400° C., or greater than or equal to402.5° C. Some embodiments may comprise exposing a sensor beingfabricated to a temperature of less than or equal to 405° C., less thanor equal to 402.5° C., less than or equal to 400° C., less than or equalto 397.5° C., less than or equal to 395° C., less than or equal to392.5° C., less than or equal to 390° C., less than or equal to 387.5°C., less than or equal to 385° C., or less than or equal to 382.5° C.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 380° C. and less than or equal to 400° C., orgreater than or equal to 395° C. and less than or equal to 405° C.).Other ranges are also possible. The sensor may be exposed to atemperature in one or more of the above-referenced ranges by, forinstance, a furnace, a rapid thermal annealer, and/or an oven.

A sensor being fabricated may be exposed to an elevated temperature to avariety of suitable times. In some embodiments, a sensor is exposed to atemperature in one or more of the above-referenced ranges for a periodof time of greater than or equal to 1 minute, greater than or equal to1.2 minutes, greater than or equal to 1.4 minutes, greater than or equalto 1.6 minutes, greater than or equal to 1.7 minutes, greater than orequal to 1.8 minutes, greater than or equal to 1.9 minutes, greater thanor equal to 2 minutes, greater than or equal to 2.1 minutes, greaterthan or equal to 2.2 minutes, greater than or equal to 2.3 minutes,greater than or equal to 2.4 minutes, greater than or equal to 2.6minutes, greater than or equal to 2.8 minutes, greater than or equal to3 minutes, greater than or equal to 3.25 minutes, greater than or equalto 3.5 minutes, greater than or equal to 3.75 minutes, greater than orequal to 4 minutes, greater than or equal to 4.5 minutes, greater thanor equal to 5 minutes, greater than or equal to 6 minutes, or greaterthan or equal to 8 minutes. In some embodiments, a sensor is exposed toa temperature in one or more of the above-referenced ranges for a periodof time of less than or equal to 10 minutes, less than or equal to 8minutes, less than or equal to 6 minutes, less than or equal to 5minutes, less than or equal to 4.5 minutes, less than or equal to 4minutes, less than or equal to 3.75 minutes, less than or equal to 3.5minutes, less than or equal to 3.25 minutes, less than or equal to 3minutes, less than or equal to 2.8 minutes, less than or equal to 2.6minutes, less than or equal to 2.4 minutes, less than or equal to 2.3minutes, less than or equal to 2.2 minutes, less than or equal to 2.1minutes, less than or equal to 2 minutes, less than or equal to 1.9minutes, less than or equal to 1.8 minutes, less than or equal to 1.7minutes, less than or equal to 1.6 minutes, less than or equal to 1.4minutes, or less than or equal to 1.2 minutes. Combinations of theabove-referenced ranges are also possible (e.g., greater than or equalto 1 minute and less than or equal to 10 minutes, or greater than orequal to 1.9 minutes and less than or equal to 2.1 minutes). Otherranges are also possible.

It should be understood that the values in the preceding paragraph mayrefer to the amount of time that a sensor being fabricated is exposed toa single temperature in one or more of the preceding ranges and/or mayrefer to the amount of time that a sensor being fabricated is exposed toany temperature in one or more of the above-referenced ranges (e.g., thetotal amount of time that the sensor is exposed to any temperature ofgreater than or equal to 380° C. and less than or equal to 400° C.).

When a sensor being fabricated is exposed to an elevated temperature, itmay also be exposed to an ambient environment that assists with theformation of ohmic contacts between the electrode material therein andthe nanowires therein. By way of example, the sensor may besimultaneously exposed to an elevated temperature and a forming gas. Theforming gas may comprise and/or consist of a mixture of hydrogen andnitrogen. Hydrogen may make up greater than or equal to 1 wt %, greaterthan or equal to 2 wt %, greater than or equal to 3 wt %, greater thanor equal to 4 wt %, greater than or equal to 5 wt %, greater than orequal to 6 wt %, greater than or equal to 7 wt %, greater than or equalto 8 wt %, or greater than or equal to 9 wt % of the mixture. Hydrogenmay make up less than or equal to 10 wt %, less than or equal to 9 wt %,less than or equal to 8 wt %, less than or equal to 7 wt %, less than orequal to 6 wt %, less than or equal to 5 wt %, less than or equal to 4wt %, less than or equal to 3 wt %, or less than or equal to 2 wt % ofthe mixture. Combinations of the above-referenced ranges are alsopossible (e.g., greater than or equal to 1 wt % and less than or equalto 10 wt % hydrogen). Other ranges are also possible.

The presence of ohmic contacts may be determined by generating an IVcurve according to the technique for generating an IV curve describedabove with respect to the on/off ratio. If the IV curve is linear and/orsubstantially linear, then ohmic contacts are considered to have beenformed.

In some embodiments, a sensor as a whole may be configured to sense oneor more analytes of interest in a particularly desirable manner. Forinstance, a sensor may respond to a relatively low level of analyte in amanner that is reproducible, predictable, and/or observable. In someembodiments, the concentration of an analyte in a fluid may bedetermined by the magnitude of a change in equivalent surface potentialof a nanowire placing a pair of electrodes in electrical communication.The change in equivalent surface potential of the nanowire may bedetermined by a measuring a change in the current across the pair ofelectrodes and then dividing the measured change in current by thetransconductance of the nanowire. The change in current across the pairof electrodes may be measured at a known applied voltage and with theuse of a picoammeter. The transconductance of the nanowire may bedetermined by: (1) concurrently applying a 0.1 V potential across thepair of electrodes and varying the potential applied to a water gateelectrode between −0.5 V and 0.5 V; and (2) plotting the measuredcurrent across the pair of electrodes as a function of the potentialapplied to the water gate electrode; and (3) identifying the maximumslope in this plot as the transconductance of the nanowire.

In some embodiments, a sensor exhibits a change in equivalent surfacepotential upon exposure to an analyte having an absolute value ofgreater than or equal to 0.005 V, greater than or equal to 0.006 V,greater than or equal to 0.007 V, greater than or equal to 0.008 V,greater than or equal to 0.009 V, greater than or equal to 0.01 V,greater than or equal to 0.015 V, greater than or equal to 0.02 V,greater than or equal to 0.025 V, greater than or equal to 0.03 V,greater than or equal to 0.04 V, greater than or equal to 0.05 V,greater than or equal to 0.06 V, or greater than or equal to 0.08 V. Insome embodiments, a sensor exhibits a change in equivalent surfacepotential upon exposure to an analyte having an absolute value of lessthan or equal to 0.1 V, less than or equal to 0.08 V, less than or equalto 0.06 V, less than or equal to 0.05 V, less than or equal to 0.04 V,less than or equal to 0.03 V, less than or equal to 0.025 V, less thanor equal to 0.02 V, less than or equal to 0.015 V, less than or equal to0.01 V, less than or equal to 0.009 V, less than or equal to 0.008 V,less than or equal to 0.007 V, or less than or equal to 0.006 V.Combinations of the above-referenced ranges are also possible (e.g.,greater than or equal to 0.005 V and less than or equal to 0.1 V). Itshould be understood that the ranges above may refer to positive changesin equivalent surface potential or negative changes in equivalentsurface potential. Accordingly, further examples of suitable rangesinclude, for example, greater than or equal to −0.005 V and less than orequal to 0.005 V, greater than or equal to −0.01 V and less than orequal to 0.01 V, or greater than or equal to −0.1 V and less than orequal to 0.1 V. Other ranges are also possible.

As described elsewhere herein, the sensors described herein may besuitable for sensing a variety of analytes in a variety of fluids. Insome embodiments, the fluid is a bodily fluid and/or comprises a bodilyfluid. For instance, the fluid may comprise a bodily fluid (e.g., asolid bodily fluid, a viscous bodily fluid) that is resuspended inanother fluid (e.g., a viral transport media, a buffered salt solution).The sensor may be suitable for sensing an analyte in a human bodilyfluid of a human and/or in a non-human, animal bodily fluid.Non-limiting types of suitable bodily fluids include types of blood(e.g., venous whole blood, capillary whole blood), components of blood(e.g., plasma, serum), urine, saliva, tears, cerebro-spinal fluid, nasalsecretions, and/or nasopharyngeal secretions. The bodily fluid may beobtained by, e.g., a finger stick. It is also possible for a bodilyfluid to be obtained by collection using a swab.

In some embodiments, a sensor described herein may sense an analyte in afluid via an electrostatic interaction. By way of example, a chargedanalyte may experience electrostatic attraction to a nanowire and/or ablocking layer disposed thereon. This electrostatic attraction may causethe analyte to deposit on the nanowire and/or blocking layer. In someembodiments, the analyte is a charged molecule, such as a chargedbiological polymer and/or a charged biological small molecule.Non-limiting examples of suitable analytes (e.g., charged analytes)include proteins (e.g., GFAP, UCH-L1, S100β, ICH, NFL-1), peptides,nucleic acids (e.g., DNA, RNA, PNA), lipids, carbohydrates, smallmolecules, and derivatives of the foregoing.

The sensors described herein may be suitable for detecting one or morecharacteristics of a patient based on the presence or absence of one ormore analytes in a fluid obtained from the patient. Some methods maycomprise employing the sensors described herein for this purpose. By wayof example, a method may comprise exposing a sensor to a fluid. Thesensor may then undergo a detectable change in one or more properties(e.g., equivalent surface potential), which may be indicative of one ormore properties of the fluid (e.g., of the concentration and/or presenceof an analyte therein). In some embodiments, the sensor may output asignal indicative of one or more properties of the fluid (e.g., it mayoutput a detectable change in equivalent surface potential that isindicative of the concentration and/or presence of an analyte, such as aprotein, in the fluid).

One example of a characteristic of a patient that may be detected iswhether or not the patient has experienced traumatic brain injury (TBI).Without wishing to be bound by any particular theory, it is believedthat TBI is a non-degenerative, non-congenital insult to the brain froman external mechanical force, which may possibly lead to permanent ortemporary impairment of cognitive, physical, and/or psychosocialfunctions. It is also believed that TBI may cause a diminished oraltered state of consciousness. A closed brain injury such as TBI may becaused by a rapid acceleration or deceleration in forward, backward,and/or rotational movement of the brain inside the skull that results inbruising and/or tearing of brain tissue and/or blood vessels. It isbelieved that the most common cause of closed brain injuries are caraccidents, falls, and sports related injuries. It is also believed thata brain injury can also be inflicted by oneself or another (e.g., in thecase of shaken baby syndrome). Early diagnosis of traumatic brain injuryis believed to facilitate the early verification that no intracranialbleeding has occurred as a result of the injury. Patients who experiencesignificant trauma to the head may be at risk of bleeding in or aroundthe brain (e.g., of having an intracranial hemorrhage, IH). Forinstance, this may be a concern in patients who present to the EmergencyDepartment (ED) after an accident, assault, or fall.

When the sensors described herein are employed to sense whether or not apatient has TBI, they may be configured to sense one or more biomarkersfor TBI in a bodily fluid from the patient (e.g., in serum from thepatient). Without wishing to be bound by any particular theory, it isbelieved that these include GFAP, UCH-L1, S100β, ICH, and NFL-1.

Example 1

This Example describes an exemplary process for forming an electricallyinsulating layer disposed a pair of electrodes. It is noted that asimilar process may also be employed to form other layers from aphotoresist (e.g., a passivating layer, a layer formed during onefabrication step to appropriately position one or more componentsthereof but removed from the sensor during a subsequent fabricationstep).

First, the substrate and components disposed thereon are prepared forphotoresist deposition. This is accomplished by rinsing the substrateand components disposed thereon with solvents, and then drying thesubstrate. Next, the substrate and components disposed thereon areheated to remove any residual water.

After cleaning, the photoresist is applied to the substrate andcomponents disposed thereon and prepared for patterning. SU-8 TF 6000.5(a negative photoresist) is applied to the substrate such that it coversapproximately 50% of its diameter, after which the substrate is spun todistribute the photoresist across its surface. Next, the substrate andcomponents disposed thereon are soft baked, and then allowed to cool.

Then, portions of the photoresist are patterned by a photolithographyprocess. First, the portions desired to be retained are exposed to lightat a wavelength that will cause the photoresist to undergo a chemicalreaction. After exposure, the substrate and components disposed thereonare baked. During this period of time, the image of the pattern ofportions of the photoresist exposed to the light may become visible.Then, the substrate and components disposed thereon are removed from thehot plate and allowed to cool.

After patterning, the portions of the photoresist so patterned areremoved from the substrate. The substrate and components disposedthereon are immersed in SU-8 developer, during which gentle agitation isapplied (e.g., by use of an orbital shaker). Then, the wafer andcomponents disposed thereon are removed from the SU-8 developer, andsprayed and washed with fresh SU-8 developer. After this step, thesubstrate and components disposed thereon are rinsed with a solvent andthen dried.

Next, photoresist residue exposed to light during the patterning processbut not removed by the subsequent development process is removed by anoxygen plasma etching process. The wafer and components disposed thereonare exposed to an oxygen plasma.

Finally, the substrate and components disposed thereon (including thephotoresist not exposed to light and still positioned on the substrate)are hard baked. The hard bake time may be adjusted upwards or downwardsif peeling of the photoresist is observed.

Example 2

This Example describes an exemplary process for disposing a wire bondingcomposition on a pair of electrodes. It is noted that a similar processmay also be employed to form other components with the assistance ofphotolithography (e.g., electrodes, a passivating layer).

First, the photoresist is applied to the substrate and componentsdisposed thereon and prepared for patterning. AZ-5214E-IR (a positivephotoresist) is applied to the substrate such that it coversapproximately 50% of the its diameter, after which the substrate is spunto distribute the photoresist across its surface. Next, the substrateand components disposed thereon are soft baked, and then allowed tocool.

Then, portions of the photoresist are patterned by a photolithographyprocess. First, the portions desired to be removed are exposed to lightat a wavelength that will cause the photoresist to undergo a chemicalreaction.

After patterning, the portions of the photoresist so patterned areremoved from the substrate. The substrate and components disposedthereon are immersed in a mixture of AZ 400K developer and deionizedwater. The immersion time should be selected to allow for removal of thephotoresist exposed to the light. After this step, the substrate andcomponents disposed thereon are rinsed with deionized water and thendried. Finally, the substrate and components disposed thereon are dried.

Next, the portions of the electrodes exposed by the removal of thephotoresist are prepared for deposition of the wire bonding composition.The passivation layer is removed from the electrode surface by dippingthe substrate and components disposed thereon in a solution having a 6:1ratio of hydrofluoric acid to ammonium fluoride for 10 to 20 seconds.After removal of the substrate and components disposed thereon from thesolution, the substrate and components disposed thereon are rinsed withdeionized water, dried, and then heated to remove any residual water.Then, the substrate and components disposed thereon are transferred to avacuum chamber.

Once in the vacuum chamber, the wire bonding composition is depositedonto the exposed electrode surface. Electron beam vacuum deposition isperformed to first deposit a titanium layer having at thickness of 10nm±1 nm and a gold layer having a thickness of 250 nm±25 nm. Portions ofthe titanium and gold layers not disposed directly on the electrode arethen removed by placing the substrate and components disposed thereon inan acetone bath for 1 to 3 hours, and then rinsing with acetone.

Example 3

This Example describes the use of sensors comprising a pair ofelectrodes in electrical communication by a nanowire.

Two sensors were formed: one sensor comprising silicon nanowires (SensorA), and one sensor comprising silicon nanowires comprising(3-aminopropyl)triethoxysilane-functionalized surfaces (Sensor B). Eachwas exposed to a series of decreasing values of pH, during which thecurrent across the pair of electrodes was measured. FIGS. 20-21 show theresult of this experiment. From both FIGs. it is apparent that Sensor Bdisplayed an increased sensitivity to changes in pH in comparison toSensor A when the current through the nanowire was measured (as shown inFIG. 20) but that the two sensors showed similar variation in equivalentsurface potential with pH (as shown in FIG. 21). It is believed thatSensor B exhibited a linear response to changes in pH over a wide rangeof pH values due to the presence of both —OH and —NH₂ groups on itssurface, both of which can undergo protonation and deprotonationreactions as the pH is changed. It is believed that Sensor A exhibited aresponse to changes in pH similar to that of pure silicon oxide.

Two further sensors were formed: one including nanowires havinganti-S100β antibody-functionalized surfaces of the nanowire (Sensor C)and one including nanowires having anti-DDK antibody-functionalizedsurfaces of the nanowire (Sensor D). Sensors C and D were first exposedto unmodified plasma and then exposed to plasma spiked with S100β at alevel of 2.5 ng/mL. FIG. 22 shows the equivalent surface potential as afunction of time for both sensors (the sensors were exposed to theS100β-spiked plasma at the time point of 260 seconds). As can be seenfrom FIG. 22, both Sensors C and D exhibited an increase in equivalentsurface potential upon exposure to the spiked plasma. The equivalentsurface potential for Sensor C remained relatively constant thereafter,while that of Sensor D continued to increase. It is believed that theinitial increase in equivalent surface potential of Sensors C was due tothe change in composition of the fluid to which it is was exposed, andthat the lack of change in equivalent surface potential thereafter isindicative of a lack of specific binding. It is believed that theincrease in equivalent surface potential with time for Sensor D isindicative of continuous specific binding of S100β to the nanowiretherein, and that the rate of change in equivalent surface potential isdirectly dependent on the binding constant of S100β to the nanowire andthe concentration of S100β in the fluid to which Sensor D was exposed.

Example 4

This Example describes sensors comprising a pair of electrodes inelectrical communication by a functionalized nanowire.

Two types of sensors were formed: a first type of sensor comprisingsilicon nanowires comprising surfaces functionalized withanti-SARS-CoV-2 spike protein antibodies (Sensor Type E), and a secondsensor comprising silicon nanowires comprising surfaces functionalizedwith control antibodies (Sensor Type F). Sensors of each type wereexposed to human saliva comprising SARS-CoV-2 spike protein at varyinglevels of concentration therein. FIG. 23 shows the equivalent surfacepotential of these sensors as a function of time. During the time scaleover which the measurements shown in FIG. 23 were made, the change inthis equivalent surface potential with time is believed to beproportional to the initial rate at which the SARS-CoV-2 spike proteinbonds to the silicon nanowires. From FIG. 23, it is thus apparent thatthe change in equivalent surface potential with time varied with theconcentration of the SARS-CoV-2 spike protein in the fluid to which thesensors were exposed for Sensor Type E, indicating that the rate ofbinding of the SARS-CoV-2 spike protein to the silicon nanowiresdepended on its concentration in the fluid to which the sensors wereexposed. By contrast, the sensors of Sensor Type F exhibited a change inequivalent surface potential with time that was relatively independentof the concentration of SARS-CoV-2 spike protein in the fluid to whichthey were exposed, indicating that little or no binding of theSARS-CoV-2 spike protein to the silicon nanowires occurred.

Accordingly, it is believed that sensors comprising surfacesfunctionalized with anti-SARS-CoV-2 spike protein antibodies can beemployed to detect the presence of such antibodies in a fluid and/or todetermine their concentration therein.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, kit, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,kits, and/or methods, if such features, systems, articles, materials,kits, and/or methods are not mutually inconsistent, is included withinthe scope of the present invention.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to thecontrary, in any methods claimed herein that include more than one stepor act, the order of the steps or acts of the method is not necessarilylimited to the order in which the steps or acts of the method arerecited.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

What is claimed is:
 1. A sensor, comprising: a plurality of pairs ofelectrodes; and a plurality of nanowires, wherein for greater than orequal to 10% of the pairs of electrodes, the two electrodes making upthe pair are in electrical communication by exactly one nanowire.
 2. Amethod of depositing a plurality of nanowires onto a substrate,comprising: expelling a fluid comprising the plurality of nanowires froma nozzle onto the substrate; allowing at least a portion of the fluid toevaporate; replenishing at least a portion of the evaporated fluid byexpelling a further amount of the fluid from the nozzle; and holding thefluid comprising the plurality of nanowires in contact with thesubstrate for a time period of greater than or equal to 0.2 sec, whereinthe fluid is in contact with both the substrate and the nozzle duringthe holding, replenishing and evaporation steps.
 3. A method as in claim2, wherein the method comprises forming a sensor comprising greater thanor equal to 10 and fewer than or equal to 40 pairs of electrodes.
 4. Amethod as in claim 2, wherein the plurality nanowires has a length ofgreater than or equal to 5 microns and less than or equal to 50 microns.5. A method as in claim 2, wherein the plurality of nanowires comprisessingle-crystalline silicon.
 6. A method as in claim 2, wherein theplurality of nanowires comprises nanowires having charged surfacesand/or comprises a binding entity.
 7. A method as in claim 2, whereinthe plurality of nanowires comprises a binding entity for a biomarkerfor brain injury.
 8. A method as in claim 2, wherein the plurality ofnanowires comprises a binding entity for small-molecule biomarker,lipids, and/or a viral protein.
 9. A method as in claim 8, wherein theviral protein is a human viral protein, a non-human animal viralprotein, and/or a plant viral protein.
 10. A method as in claim 8,wherein the viral protein is a SARS-CoV-2 protein, an influenza virusprotein, a zika virus protein, a parainfluenza virus protein, a HIV1virus protein, and/or a HHV virus protein.
 11. A method as in claim 2,wherein the method comprises forming a sensor comprising a blockinglayer.
 12. A method as in claim 11, wherein the blocking layer isdisposed on the plurality of nanowires.
 13. A method as in claim 11,wherein the blocking layer comprises a protein.
 14. A method as in claim11, wherein the blocking layer comprises a stabilizer which is removedupon contact with liquid.
 15. A method as in claim 2, wherein the methodcomprises forming a sensor, further comprising exposing the sensor as toa fluid.
 16. A method as in claim 15, wherein the fluid comprises abodily fluid.
 17. A method as in claim 16, wherein the bodily fluid isblood, is plasma, is saliva, is tears, is urine, is a nasal fluid, is anasopharyngeal fluid, was obtained through finger stick, was collectedusing a swab, and/or comprises a solid or viscous sample resuspended inanother fluid.
 18. A method as in claim 2, wherein the method comprisesforming a sensor, and wherein the sensor is configured to output asignal indicative of a concentration of the protein in the fluid.
 19. Amethod as in claim 2, wherein the evaporation step and the replenishingstep are performed simultaneously, and/or wherein the evaporation stepand the holding step are performed simultaneously.
 20. A method as inclaim 2, wherein the substrate is heated during the evaporation step.21. A method as in claim 2, wherein the fluid comprises an organicsolvent with boiling point less than 120° C.
 22. A method as in claim 2,further comprising depositing a photoresist on the nanowires.
 23. Amethod as in claim 2, further comprising depositing a metal on thenanowires to form an electrode.
 24. A method as in claim 23, furthercomprising heating the electrode and the nanowires, and wherein heatingthe electrode and the nanowires causes the formation of an ohmic contacttherebetween.
 25. A method as in claim 23, further comprising depositinga photoresist on the electrode.
 26. A method as in claim 25, wherein thephotoresist comprises an SU8, comprises a polyimide, and/or is apoly-imide based photoresist.
 27. A method as in claim 23, furthercomprising depositing a second metal on the metal to form an electrodeconfigured to be in electrical communication with an environmentexternal to the sensor.
 28. A fluidic device comprising a plurality ofsensors formed by the method of claim
 2. 29. A method as in claim 2,wherein the method comprises forming a sensor, and wherein the sensorcomprises a plurality of pairs of electrodes that are equidistant from acenter point.
 30. A method as in claim 2, wherein the method comprisesforming a sensor, and wherein the sensor comprises two or more groups ofnanowires that are functionalized with different chemistries.